120 COMPARATIVE ANATOMY. 



muscles, Fig. 98, Ma, T), supplied by the third division of the 

 trigeminal. All these muscles, which may be derived from the 

 adductor of the mandible of Elasmobranchs and Ganoids, arise 

 from the auditory region of the skull. 



Amniota. With the simplification of the visceral skeleton in 

 Amniota, there is a considerable reduction of the musculature 

 belonging to it. All muscles connected with branchial respiration 

 are of course wanting, and the ventral trunk-muscles, as men- 

 tioned above, are always interrupted in their forward extension 

 by the sternum and pectoral arch. At the same time, the 

 muscles along the neck and on the floor of the mouth met with in 

 Amphibia are present here also; they are the mylo-, sterno-, 

 omo-, and genio-hyoid, as well as the hyoglossus and genio- 

 glossus. To these may be also added a sterno-thyroid, and a 

 thyro-hyoid, continued forwards as a prolongation of the former. 



The stylo-hyoid, stylo-glossus, and stylo-pharyngeus of Mammals, 

 arising from the styloid process and stylo-hyoid ligament, and undergoing 

 numerous variations, are neomorphs. They are supplied partly by the facial, 

 partly by the glossopharyngeal, and act as retractors of the tongue and 

 levators of the pharynx and hyoid. 



The muscles of the jaws resemble those of Amphibia, 

 although, especially in the case of the pterygoids, they are much 

 more sharply differentiated, and are throughout more strongly 

 developed. (A secondary subdivision of the muscles may occur 

 in Birds and Reptiles, as for instance in the case of the temporal 

 muscle.) 



The facial muscles, forming a marked feature for the first time 

 in Mammals, arise originally in the neighbourhood of the eyes, 

 mouth, nose, and ears, around which they are principally grouped 

 throughout life ; they are thus connected with the most important 

 organs of sense. They are supplied by the facial nerve, and attain 

 their greatest development in Primates. 



Following in the lines laid down by Gegenbaur in his Lehrbuch der 

 Anatomic des Menschen on the origin of the facial muscles, G. Huge has made 

 detailed researches on the facial musculature of Lemurs, from which he arrives 

 at the following results. 



The fact that all the muscles supplied by the facial nerve belong to 

 the same series indicates that those related to the visceral skeleton, and 

 having originally nothing to do with the face, which are supplied by the same 

 nerve, must have shifted upwards from the region of the lower jaw and neck, 

 so as to come into close relation with the soft "parts surrounding the apertures 

 of the ear and mouth, that is, to the secondarily-formed lips and external 

 ear. From these points they extended further, taking on new relations to the 

 eye, nasal aperture, and frontal and temporal regions. The muscu- 

 lature further extended to the parietal region, the parts of it in front of the 

 aperture of the ear arising from the frontal and temporal regions, those behind 

 it from the occipital region. The upward change of position of the musculature 

 thus took place along two lines, in front of, and behind the ear, as is 

 proved by its iiiuervation, to be described directly. 



