Deficits of masticatory movements caused by lesions in the orofacial somatosensory cortex of the awake cat

The purpose of this study was to determine the role of somatosensory cortex (SI) in the control of orofacial movements during eating.We identified perioral and tongue projection regions of the cat SI and destroyed cells in one region by injecting kainic acid. The effects on orofacial behavior were then studied over a period of 4-6 weeks. Cats with unilateral lesions in the perioral region (PL-cats) dropped food from the contralateral side of the mouth in the early phase. Failure in erection of the contralateral whisker hairs during masticatory movements and delay of the masticatory start were observed throughout the experimental period. Furthermore, in the late phase, PL-cats showed prolongations of the masticatory and food intake periods, which were accompanied by the increase in the number of swallows and chewing cycles. Cats with unilateral lesions in the tongue region (TL-cats) showed the prolongation of the masticatory period in the early phase, which was accompanied by the increase in the number of swallows and chewing cycles. TL-cats did not show the prolongation of the food intake period and failure in erection of the contralateral whisker hairs. In both PL- and TL-cats, masticatory and swallowing rhythms were normal.     

Mastication-related neurons in the orofacial first somatosensory cortex of awake cats

In the orofacial area of the first somatosensory cortex (SI), we recorded single unit activity from 699 neurons in 11 awake cats. Fifty-two percent (362/699) were mastication-related neurons (MRNs) showing activity related to some aspects of masticatory movements. MRNs were divided into three types by their activity patterns: (1) the rhythmical type, showing rhythmical bursts in pace with the masticatory rhythm; (2) the sustained type, showing a sustained firing during the period of taking food and (3) the transient (biting) type, showing intense discharges in coincidence with biting hard food. MRNs had mechanoreceptive fields in the perioral, tongue, periodontal and mandibular regions. The activities of perioral rhythmical-MRNs, mandibular transient-MRNs, tongue rhythmical-MRNs and periodontal transient-MRNs were correlated with food texture, while perioral rhythmical-MRNs, perioral sustained-MRNs and tongue sustained-MRMs were not. Both facial and intraoral MRNs were scattered throughout the facial and intraoral projection areas in SI. These findings provide evidence that the orofacial SI monitors masticatory movements for food ingestion.     

Cortical control of mastication in cats. 2. Deficits of masticatory movements following a lesion in the motor cortex

Our previous study suggested that area P in the lateral wall of the presylvian sulcus and MA (masticatory cortex) in the rostral part of the orbital gyrus play an important role in execution of mastication. The aim of this present study is to examine if changes in orofacial behaviors and masticatory movements occur in cats with lesions of area P. First, we explored the locations in area P through the use of single unit recording and ICMS (intracortical microstimulation). Since mastication related neurons (MRNs) with the mechanical receptive field (RF) in facial or intraoral region were intermingled in area P, we performed either a partial or entire lesion in area P by injections of 2 microl or 4 microl of 0.1% kainic acid. Cats with the entire lesion in area P showed a decrease of food intake rates associated with abnormal tongue protrusion and wide jaw-opening, fluctuation of masticatory start, and prolongation of masticatory and food intake periods. Abnormal movements of tongue and jaw did not recover, although their prolongation and fluctuation returned to normal levels in one month. On the other hand, all deficits evoked by cats with the partial lesion recovered in about one month. In cats with the partial and entire lesions, masticatory rhythm remained normal. These findings suggest that area P may regulate accurate and suitable tongue and jaw movements during mastication depending on cortical processing.     

Cortical control of mastication in the cat: properties of mastication-related neurons in motor and masticatory cortices

The aim of this study is to examine mastication-specific activity of orofacial neurons in the motor and masticatory cortices of the awake cat. We examine properties of mastication-related neurons (MRNs) in masticatory (MA, the rostral region of the orbital gyrus) and motor (area P, the lateral wall of the presylvian sulcus) cortical areas that are related to mastication of cats. MRNs in MA and area P had in common mechanoreceptive fields (RFs) in perioral, mandibular and lingual regions, and many MRNs had bilateral RFs in the tongue and mandibular regions. Facial RF size was the largest in area P. Eleven percent of MRN recording sites in MA, and 43% in area P evoked various motor effects with the use of intracortical microstimulation (ICMS). MRNs of the pre-movement type showing activities prior to mastication, or masticatory or lingual EMG, were 14% in MA and 45% in area P. Based on wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injection into area P and MA, cortico-cortical connections were examined. After the unilateral area P injection, were reciprocal connections between the contralateral area P and bilateral MA were demonstrated. After the unilateral MA injection, there were reciprocal connections between the contralateral MA, bilateral area P and bilateral orofacial SI (the orofacial region of the first somatosensory area). These findings suggest that accurate masticatory movements may be executed by the cortical processing in MA and area P.     

Cortical control of mastication in the cat: properties of mastication-related neurons in motor and masticatory cortices

The aim of this study is to examine mastication-specific activity of orofacial neurons in the motor and masticatory cortices of the awake cat. We examine properties of mastication-related neurons (MRNs) in masticatory (MA, the rostral region of the orbital gyrus) and motor (area P, the lateral wall of the presylvian sulcus) cortical areas that are related to mastication of cats. MRNs in MA and area P had in common mechanoreceptive fields (RFs) in perioral, mandibular and lingual regions, and many MRNs had bilateral RFs in the tongue and mandibular regions. Facial RF size was the largest in area P. Eleven percent of MRN recording sites in MA, and 43% in area P evoked various motor effects with the use of intracortical microstimulation (ICMS). MRNs of the pre-movement type showing activities prior to mastication, or masticatory or lingual EMG, were 14% in MA and 45% in area P. Based on wheat germ agglutinin–horseradish peroxidase (WGA-HRP) injection into area P and MA, cortico-cortical connections were examined. After the unilateral area P injection, were reciprocal connections between the contralateral area P and bilateral MA were demonstrated. After the unilateral MA injection, there were reciprocal connections between the contralateral MA, bilateral area P and bilateral orofacial SI (the orofacial region of the first somatosensory area). These findings suggest that accurate masticatory movements may be executed by the cortical processing in MA and area P.     

Organization of cortical processing for facial movements during licking in cats

We proposed that cortical organization for the execution of adequate licking in cats was processed under the control of two kinds of affiliated groups for face and jaw & tongue movements (Hiraba H, Sato T. 2005A. Cerebral control of face, jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding Somatosens Mot Res 22:307-317). We assumed the cortical organization for face movements from changes in MRN (mastication-related neuron) activities recorded at area M (motor cortex) and orofacial behaviors after the lesion in the facial SI (facial region in the primary somatosensory cortex). Although we showed the relationship between facial SI (area 3b) and area M (area 4delta), the property of area C (area 3a) was not fully described. The aim of this present study is to investigate the functional role of area C (the anterior part of the coronal sulcus) that transfers somatosensory information in facial SI to area M, as shown in a previous paper (Hiraba H. 2004. The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats Somatosens Mot Res 21:87-97). We examined the properties of MRNs in area C and changes in orofacial behaviors after the area C or area M lesion. MRNs in area C had in common RFs in the lingual, perioral, and mandibular parts, and activity patterns of MRNs showed both post- and pre-movement types. Furthermore, cats with the area C lesion showed similar disorders to cats with the area M lesion, such as the dropping of food from the contralateral mouth, prolongation of the period of ingestion and mastication, and so on. From these results, we believe firmly the organization of unilateral cortical processing in facial SI, area C, and area M for face movements during licking.     

Organization of cortical processing for facial movements during licking in cats

We proposed that cortical organization for the execution of adequate licking in cats was processed under the control of two kinds of affiliated groups for face and jaw & tongue movements (Hiraba H, Sato T. 2005A. Cerebral control of face, jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding Somatosens Mot Res 22:307–317). We assumed the cortical organization for face movements from changes in MRN (mastication-related neuron) activities recorded at area M (motor cortex) and orofacial behaviors after the lesion in the facial SI (facial region in the primary somatosensory cortex). Although we showed the relationship between facial SI (area 3b) and area M (area 4δ), the property of area C (area 3a) was not fully described. The aim of this present study is to investigate the functional role of area C (the anterior part of the coronal sulcus) that transfers somatosensory information in facial SI to area M, as shown in a previous paper (Hiraba H. 2004. The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats Somatosens Mot Res 21:87--97). We examined the properties of MRNs in area C and changes in orofacial behaviors after the area C or area M lesion. MRNs in area C had in common RFs in the lingual, perioral, and mandibular parts, and activity patterns of MRNs showed both post- and pre-movement types. Furthermore, cats with the area C lesion showed similar disorders to cats with the area M lesion, such as the dropping of food from the contralateral mouth, prolongation of the period of ingestion and mastication, and so on. From these results, we believe firmly the organization of unilateral cortical processing in facial SI, area C, and area M for face movements during licking.     

Cerebral control of face,jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding

Mastication is achieved by cooperation among facial, masticatory, and lingual muscles. However, cortical control in cats for the masticatory performance is processed by two systems: facial movement processed by facial SI (the first somatosensory cortex), area C, and area M (motor areas), and jaw and tongue movements performed by intraoral SI, masticatory area, and area P (motor area). In particular, outputs from area P organized in the corticobulbar tract are projected bilaterally in the brainstem. In this present study, the aim is to explore changes in the regional cerebral blood flow (rCBF) in the facial SI, area M, and area P during trained lateral feeding (licking or chewing from the right or left side) of milk, fish paste, and small dry fish. The rCBF in area M showed contralateral dominance, and rCBF in area P during chewing or licking from the right or left side was almost the same value. Furthermore, activities of genioglossus and masseter muscles in the left side showed almost the same values during licking of milk and of fish paste, and chewing of small dry fish during lateral feeding. These findings suggest that the cortical process for facial, jaw, and tongue movements may be regulated by the contralateral dominance of area M and the bilateral one of area P.     

Cerebral control of face, jaw, and tongue movements in awake cats: changes in regional cerebral blood flow during lateral feeding

Mastication is achieved by cooperation among facial, masticatory, and lingual muscles. However, cortical control in cats for the masticatory performance is processed by two systems: facial movement processed by facial SI (the first somatosensory cortex), area C, and area M (motor areas), and jaw and tongue movements performed by intraoral SI, masticatory area, and area P (motor area). In particular, outputs from area P organized in the corticobulbar tract are projected bilaterally in the brainstem. In this present study, the aim is to explore changes in the regional cerebral blood flow (rCBF) in the facial SI, area M, and area P during trained lateral feeding (licking or chewing from the right or left side) of milk, fish paste, and small dry fish. The rCBF in area M showed contralateral dominance, and rCBF in area P during chewing or licking from the right or left side was almost the same value. Furthermore, activities of genioglossus and masseter muscles in the left side showed almost the same values during licking of milk and of fish paste, and chewing of small dry fish during lateral feeding. These findings suggest that the cortical process for facial, jaw, and tongue movements may be regulated by the contralateral dominance of area M and the bilateral one of area P.     

Mastication in the musk shrew,Suncus murinus (mammalia,Soricidae)

High-speed cinematography shows that Suncus murinus (Crocidurinae) masticates fast (mean 5.5, 5–10 masticatory cycles per sec). Their grasping behavior is not stereotyped. The unilateral mandibular movements combine vertical, anteroposterior, and lateral displacements; and any masticatory sequence may include crushing, repositioning, shearing, and grinding components. Size and consistency of food influence the duration of individual chewing cycles. As food is transferred to the new working side, the chewing direction reverses, either near maximum closure or near maximum opening. An unfused mandibular symphysis permits tilting movements of the two halves of the mandible. Food may be squeezed between the lower incisors. The working side tilts outward during closing; this may improve shearing or grinding action. The closing phase is posteriorly directed. Thus, the masticatory movements of these shrews differ from those that have been described in many other mammals.     

Effects of reversible cold block of face primary somatosensory cortex on orofacial movements and related face primary motor cortex neuronal activity

Our previous studies have revealed that face primary somatosensory cortex (SI) as well as face primary motor cortex (MI) play important roles in the control of orofacial movements in awake monkeys, and that both face MI and face SI neurons may have an orofacial mechanoreceptive field and show activity related to orofacial movements. Since it is possible that the movement-related activity of face MI neurons could reflect movement-generated orofacial afferent inputs projecting to face MI via face SI, the present study used reversible cold block-induced inactivation of the monkey's face SI to determine if face MI neuronal activity related to a trained tongue-protrusion task, chewing or swallowing was dependent on the functional integrity of the ipsilateral face SI and if inactivation of face SI affects orofacial movements. The effects of face SI cold block were tested on chewing, swallowing and/or task-related activity of 73 face MI neurons. Both task and chewing and/or swallowing-related activity of most face MI neurons was independent of the functional integrity of the ipsilateral face SI since SI cold block affected the movement-related activity in approximately 25% of the neurons. Similarly, unilateral cold block of SI had very limited effects on the performance of the task and chewing, and no effect on the performance of swallowing. These findings suggest that movement-induced reafferentation via face SI may not be a significant factor in accounting for the activity of the majority of ipsilateral face MI neurons related to trained movements, chewing and swallowing.     

Effects of reversible cold block of face primary somatosensory cortex on orofacial movements and related face primary motor cortex neuronal activity

Our previous studies have revealed that face primary somatosensory cortex (SI) as well as face primary motor cortex (MI) play important roles in the control of orofacial movements in awake monkeys, and that both face MI and face SI neurons may have an orofacial mechanoreceptive field and show activity related to orofacial movements. Since it is possible that the movement-related activity of face MI neurons could reflect movement-generated orofacial afferent inputs projecting to face MI via face SI, the present study used reversible cold block-induced inactivation of the monkey's face SI to determine if face MI neuronal activity related to a trained tongue-protrusion task, chewing or swallowing was dependent on the functional integrity of the ipsilateral face SI and if inactivation of face SI affects orofacial movements. The effects of face SI cold block were tested on chewing, swallowing and/or task-related activity of 73 face MI neurons. Both task and chewing and/or swallowing-related activity of most face MI neurons was independent of the functional integrity of the ipsilateral face SI since SI cold block affected the movement-related activity in approximately 25% of the neurons. Similarly, unilateral cold block of SI had very limited effects on the performance of the task and chewing, and no effect on the performance of swallowing. These findings suggest that movement-induced reafferentation via face SI may not be a significant factor in accounting for the activity of the majority of ipsilateral face MI neurons related to trained movements, chewing and swallowing.     

Cortical control for mastication in cats: changes in masticatory movements following lesions in the masticatory cortex

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.     

Cortical control for mastication in cats: Changes in masticatory movements following lesions in the masticatory cortex

In a previous paper (Hiraba and Sato ) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0?µl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F & F, I & I or F & I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F & I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F & F, or I & I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F & F and I & I of the bilateral MA.     

The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats

The aim of the present study was to investigate the relationship between the facial region of the first somatosensory cortex (facial SI) and facial region of the motor cortex (facial MI), as the basis of orofacial behaviors during ingestion of fish paste. Area M in the ventral cortex of the cruciate sulcus that was defined as part of the facial MI by and, showed various facial twitches evoked by intracortical microstimulation (ICMS) and recorded many mastication-related neurons (MRNs). Many MRNs in area M had receptive fields (RFs) in lingual, perioral and mandibular regions. The 60% value of activity patterns of MRNs (n = 124) recorded in area M of normal cats, were the pre-SB type (the sustained and pre-movement type) that showed increased firing prior to the start of mastication and then tonic activity during the masticatory period. MRNs recorded in area M of cats with the facial SI lesion, showed a noticeable decrease in MRNs with RFs in the perioral and mandibular regions and with activity of the pre-SB type. These results strongly suggest that blocking facial SI sensory inputs evoked by mastication interferes with the relay of important facial sensory information to area M required for the appropriate manipulation of food during mastication.     

Twist and chew: three-dimensional tongue kinematics during chewing in macaque primates

Three-dimensional (3D) tongue movements are central to performance of feeding functions by mammals and other tetrapods, but 3D tongue kinematics during feeding are poorly understood. Tongue kinematics were recorded during grape chewing by macaque primates using biplanar videoradiography. Complex shape changes in the tongue during chewing are dominated by a combination of flexion in the tongue''s sagittal planes and roll about its long axis. As hypothesized for humans, in macaques during tongue retraction, the middle (molar region) of the tongue rolls to the chewing (working) side simultaneous with sagittal flexion, while the tongue tip flexes to the other (balancing) side. Twisting and flexion reach their maxima early in the fast close phase of chewing cycles, positioning the food bolus between the approaching teeth prior to the power stroke. Although 3D tongue kinematics undoubtedly vary with food type, the mechanical role of this movement—placing the food bolus on the post-canine teeth for breakdown—is likely to be a powerful constraint on tongue kinematics during this phase of the chewing cycle. The muscular drivers of these movements are likely to include a combination of intrinsic and extrinsic tongue muscles.     

The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats

The aim of the present study was to investigate the relationship between the facial region of the first somatosensory cortex (facial SI) and facial region of the motor cortex (facial MI), as the basis of orofacial behaviors during ingestion of fish paste. Area M in the ventral cortex of the cruciate sulcus that was defined as part of the facial MI by Hiraba et al. (1992 and 1993), showed various facial twitches evoked by intracortical microstimulation (ICMS) and recorded many mastication-related neurons (MRNs). Many MRNs in area M had receptive fields (RFs) in lingual, perioral and mandibular regions. The 60% value of activity patterns of MRNs (n?=?124) recorded in area M of normal cats, were the pre-SB type (the sustained and pre-movement type) that showed increased firing prior to the start of mastication and then tonic activity during the masticatory period. MRNs recorded in area M of cats with the facial SI lesion, showed a noticeable decrease in MRNs with RFs in the perioral and mandibular regions and with activity of the pre-SB type. These results strongly suggest that blocking facial SI sensory inputs evoked by mastication interferes with the relay of important facial sensory information to area M required for the appropriate manipulation of food during mastication.     

The use of the tongue and hyoid apparatus during feeding in lizards (Ctenosaura similis and Tupinambis nigropunctatus)

The use of the tongue and hyoid is examined in cineradiographic and electromyographic investigations of feeding in two species of lizards, Ctenosaura similis (Iguanidae) and Tupinambis nigropunctatus (Teiidae). In both animals food is transported through the oral cavity by regular cycles of the tongue. Tongue movements correlate with jaw and hyoid movement. Similarities between the two animals in the use of the tongue in food transport, lapping, pharyngeal packing, and pharyngeal emptying are detailed. Mechanisms of tongue protrusion are examined and it is shown that the tongue in Tupinambis is relatively more protrusible than in Ctenosaura. This difference is complementary with data on the greater reliance of Tupinambis on the tongue as a sensory organ. Tupinambis further differs from Ctenosaura in possessing a greater mobility of the hyoid. In many features of tongue use in food transport, lizards resemble mammals, supporting postulations of a basic pattern of intra-oral food transport. However, whether this pattern can be attributed to convergence or a common, primitive neural pattern of control cannot be distinguished. Lizards lack two major characteristics of mammalian food transport: regular masticatory cycles and an internal swallowing mechanism.     

Pharyngeal mastication and food transport in the carp (Cyprinus carpio L.): A cineradiographic and electromyographic study

Cyprinids constitute the largest fish family and are characterized by their pharyngeal teeth. The masticatory mechanism is still poorly understood. The complex of structures that determine the movements of pharyngeal teeth and chewing pad in the carp (Cyprinus carpio L.) is analyzed. Activities in 16 head muscles of a free-swimming carp were recorded. X-ray cinerecordings, synchronized with electromyograms, were made of the intake, transport, mastication, and deglutition of radiopaque food pellets. Metal markers allowed a detailed movement analysis. Masticatory cycles are bilaterally synchronous and show distinct crushing and grinding patterns. Direct masticatory muscles that suspend and connect the pharyngeal bones steer and stabilize the masticatory movements. Baudelot's ligament, between skull and pectoral girdle, is applied as fulcrum, effects a crucial shift of the rotation axis of the pharyngeal jaw, and transforms crushing into grinding; simultaneous abduction lengthens the grinding stroke. Body muscles supply indirectly the power for mastication; they also appear to be regulated more distantly. The epaxial muscles lift the skull and thereby the levators of the pharyngeal bones, thus transmitting high forces to the teeth. They also stretch the levator of the bone as soon as occlusion is reached and thus optimize its production of forces during grinding. The hypaxial muscles retract the pharyngeal bones indirectly during grinding and power the teeth in sliding. The chewing pad, previously assumed to be motionless, rotates rostroventrad with the skull and intensifies grinding. Respiration and mastication are mutually related. The extensive movements of the pharyngeal bones are permitted only by the simultaneous expansion of the buccopharynx and a slide-coupling in the branchial floor. Muscular pads that line the pharynx are shown to transport food toward the teeth. The constrictor pharyngis effects deglutition. Natural food, intestinal contents, and feces of the carp were analyzed with respect to the capacity for distinct masticatory operations. During the experiments pellets, barley, and worms were fed. The carp is specialized for polyphagy and this appears to be based on the profiles of the heterodont teeth rather than on drastic changes in the two preprogrammed activity patterns. Comparison of the pharyngeal jaw system in the carp and higher teleosts emphasizes the structural design for the application of large forces in this cyprinid.     

DISTRIBUTION AND INNERVATION OF FACIAL BRISTLES AND HAIRS IN THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

The distribution and anatomy of sirenian perioral bristles (modified vibrissae) and facial hairs are of interest because of their use during feeding and tactile exploration. In the present study we have identified six fields of perioral bristles on the face of the Florida manatee (T. manatus latirostris), four (U1-U4) on each side of the upper lips and oral cavity, and two (L1-L2) on each side of the lower lip pad, inside the oral cavity and rostral to the horny mandibular pad. Each field has a characteristic location, number of bristles, and range of bristle length and diameter. There is a mean of 110 (± 19) bristles per side, with no left-right differences. Branches of the infraorbital nerve innervate the bases of the largest bristles (U2 group) on the upper bristle pad, and the inferior alveolar nerve supplies the bristles of the lower bristle pad. The dorsal and ventral buccal branches of the facial nerve innervate the superficial facial musculature, which is likely to be involved in bristle eversion and other movements which constitute feeding behavior. Hair is denser in the facial region than on the remainder of the body. Within the face, hair is denser on the oral disk than on the supradisk. The oral disk contains bristle-like hair, whereas the supradisk region possesses hair that is similar in length and diameter to that on the postcranial body. The mean total of bristles and hairs per face was 1,942. Means for the subregions were 220 (± 39) bristles on the perioral bristle pads, 601 (± 115) bristlelike hairs in the oral disk region, 710 (± 229) typical hairs in the supradisk region, and 411 (± 108) typical hairs on the chin. There were no significant differences between left and right side counts. Facial hair density was inversely correlated with facial area and body size. These data provide new information on the anatomical basis of the exceptional orofacial activities characteristic of manatees during feeding and tactile exploration.