SOLIPEDA. 



725 



have the same general arrangement as in the 

 human subject. In the horse, their disposi- 

 tion is as follows, beginning with those whose 

 office is to raise the framework of the chest 

 and thus assist in inspiration. 



The scaleni differ in no remarkable respect 

 from the corresponding muscles in the human 

 body. The same may be said of the inter- 

 costal muscles, the levatores coxtarum, the ser- 

 ratus posticus superior (dorso-costien), the se r- 

 ratus posticus inferior (iombo-costien), and the 

 triangularis sterni (sterno-costien), the two latter 

 of which must be regarded as depressors of 

 the ribs, and consequently acting the part of 

 muscles of expiration. 



In all quadrupeds possessing a greater num- 

 ber of ribs, and consequently a more capacious 

 thorax than man, the attachments, of the dia- 

 phragm are found to be much further re- 

 moved from the margins of the false ribs than 

 in the human subject : nevertheless the position 

 which it occupies, and its connections in the 

 thoracic cavity, are similar in all mammiferous 

 animals. 



The walls of (he abdomen, in the horse as 

 in the generality of quadrupeds, are composed 

 of five pairs of muscles, to which the same 

 names are applicable as are bestowed upon 

 them by the anthropotomist. 



The obliquus externus abdominis (costo-ab- 

 dominien) arises, by tendinous processes that 

 indigitate with the origins of the serratus 

 rnagnus, from the external surface of all the 

 lower ribs, beginning at the fifth ; and below 

 the last rib it derives its posterior attach- 

 ment from the fascia lumborum ; from these 

 origins, it runs backwards and downwards, 

 terminating in a broad tendinous expansion, 

 the terminations of which in the linea alba, 

 os pubis, and Poupart's ligament, together 

 with the formation of the external abdominal 

 ring, are exactly as in the human subject. 



The obliquus internus (ileo-abdominien) ex- 

 hibits the usual arrangement, arising tendinous 

 and fleshy from the crest of the ileum and 

 pubic ligament, whence it mounts obliquely for- 

 wards to be inserted into the cartilages of 

 all the lower ribs as far forwards as the ensi- 

 form cartilage of the sternum. 



The rectus abdominis (sterno-pubieii) is much 

 more extensively developed in the horse than 

 in human beings. Arising from the os pubis 

 it passes forwards enclosed in its usual sheath 

 to be inserted into the ensiform cartilage and 

 into the cartilaginous terminations of the third, 

 fourth, fifth, sixth, seventh, eighth and ninth 

 ribs, and also into the sternum between the 

 cartilages of the third and fourth ribs. There 

 are even fleshy fibres derived from this muscle 

 prolonged as far forwards as the articulation 

 between the first rib and the sternum, which, 

 by the old anatomists, was regarded as a dis- 

 tinct muscle, and named " musculus in summo 

 thorace situs." 



In many of the Carnivora the rectus ab- 

 dominis is equally remarkable for its great 

 length, and in some species it is even pro- 

 longed forwards to the very anterior ex- 

 tremity of the sternum. When the recti 



are thus largely developed the pymmidales 

 do not exist. 



Anterior extremity. Muscles of the shoulder. 

 It may readily be supposed that in the 

 horse and other herbivorous quadrupeds not 

 possessed of a clavicle, and, moreover, remark- 

 able for the extreme simplicity of the struc- 

 ture of their scapular apparatus, these muscles 

 undergo important modifications in their dis- 

 position and attachments, which it will be 

 interesting to investigate. In the human 

 subject the muscles specially appropriated to 

 the movements of the shoulder are ei<jht in 

 number, viz, the serratus magnus, the pec- 

 toralis minor, the levator scapulae, the rhomboi- 

 deus, the trapezius, the owo-hyoideus, the sub- 

 clavius, and the sterno-cleido mastoideus, all of 

 which concur in producing the various move- 

 ments of which the human shoulder is sus- 

 ceptible. Of these, it will be observed, the 

 six first belong exclusively to the Scapula, 

 except the trapezius, which is inserted ex- 

 tensively into the clavicle ; whilst the opera- 

 tion of the two last is upon the clavicle only. 



In quadrupeds the shoulder is furnished 

 with the same muscles as those which are met 

 with in man, only they present differences in 

 their proportions and attachments, which are 

 dependent upon the structure of the skeleton, 

 or the particular requirements of the animal ; 

 and, moreover, they are provided with an 

 additional muscle, of which no vestiges appear 

 in our own bodies. In the horse, the ar- 

 rangement of the muscular apparatus of the 

 shoulder is as follows. 



The trapezius, in all quadrupeds destitute 

 of clavicles, or in which these bones are but 

 imperfectly developed, presents an arrange- 

 ment very different from what exists in such 

 as have the clavicles completely formed : that 

 part which would in the latter case have been 

 the clavicular portion, becomes confounded 

 with the deltoid and with the cleido-mastoid 

 (here a very distinct muscle from the sterno- 

 mastoid). From the combination of these 

 three, there usually results a single muscle, 

 which is implanted immediately into the 

 hurnerus, and which, from its attachments, 

 might be named the masto-humeralis. It is 

 this muscle which is named by Stubbs the 

 leva'or humeri proprius, and its posterior part 

 musculus ad levatorem accessorius ; and by the 

 French hippotomists muscle commun de la tete 

 de ^enclosure et du bras. This clavicular por- 

 tion of the trapezius is very distinct from the 

 scapular portion, from which it is in many 

 animals separated by the trachelo-acromial 

 muscle, to be described further on. 



In the horse, therefore, the Trapezius may 

 be said to consist of that part only which is 

 called the ascending portion in the human 

 subject, and which is inserted into the pos- 

 terior margin of the spine of the scapula. 

 The sterno-mastoid is present, but the levator 

 anguli scapuks, the cleido-mastoid, and the 

 clavicular portions of the trapezius and deltoid 

 are all replaced by the muscular expansion 

 above described, and which, taking its origin 

 from the mastoid process of the temporal bone 



3 A 3 



