SPINAL ACCESSORY NERVE. 



745 



female mammae; except, as Aristotle expresses 

 it, in such animals as resemble their mothers* : 

 that is to say, in other words, that there were 

 a few exceptional cases. Subsequent authors 

 have stated the same concerning male solipeds 

 in generalf, although none stated in what the 

 resemblance consisted, or where the mammas 

 in those furnished with them were situated ; 

 so that even Buffon asserted it as a fact, that 

 the male solipeds had no vestiges of mammas. 

 Daubenton, however, having previously dis- 

 covered the situation of these organs in the 

 male ass, was led from analogy to expect 

 their presence in the horse likewise, and soon 

 detected them, but situated in a very unusual 

 position, namely, upon the prepuce of the 

 animal. The prepuce of the stallion is found 

 to form a kind of prominent ring around the 

 aperture through which the penis is protruded, 

 and it is upon this circular protuberance, close 

 to the sides of the scrotum, that the mam- 

 mae are situated. These organs are two in 

 number (^g.518.//), situated at a distance of 

 about half an inch from each other, and are 

 easily distinguishable from the circumstance 

 of the skin being raised into a papilla around 

 each nipple, in the centre of which there is a 

 shallow depression. It would seem, however, 

 that in old horses the presence of these ru- 

 dimentary mammae becomes less apparent. 



In the mare, the mammary glands are situ- 

 ated between the thighs at a distance of about 

 nine inches in front of the vulva. The nipples 

 are only two in number, one on each side of the 

 mesial line, and their distance from each other 

 is not more than an inch and a half. As in 

 the goat and many herbivorous quadrupeds, 

 all the lactiferous ducts form, in the base of 

 each gland just above the root of the nipple, 

 a large hollow cavity, which is divided by an 

 internal septum into two chambers, one situ- 

 ated in front, and the other behind ; from 

 each chamber a separate duct is derived, which 

 passes along the nipple as far as its extremity, 

 where it terminates. The orifices of these 

 canals are situated, one behind, the other about 

 a line, apart. It is owing to the presence of 

 the reservoirs thus formed by the cavities of 

 the mammary glands, that the lacteal secretion 

 is permitted to accumulate in considerable 

 quantities, until required for the nourishment 

 of the young, or removed by human agency 

 for the purpose of procuring the milk, which 

 is frequently employed as an article of diet. 



BIBLIOGRAPHY. Buffon et Daubenton, Histoire 

 Naturelle, torn. iv. 4to. Paris, 1753. Cuvier, Anato- 

 mie Comparee. Clark, Bracy, A Series of original 

 Experiments on the Foot of the living Horse, 4to. 

 1809. Clark, Bracy, Sectional Figure of the Horse, 

 with Remarks on certain Properties of his general 

 Framing, 4to. London, 1813. Stubbs, George, The 

 Anatomy of the Horse, London, fol. 1766. Bourgelat, 

 Siemens de T Art Veterinaire. Lafosse, Cours d'Hip- 

 piatrique. Vitet, Medecine Ve'terinaire, Lyons, 1783. 



(T. Rymer Jones.} 



* Equi mammas non habent, nisi qui matri similes 

 prodiere. Arist. de Partib. Anim. lib. iv. cap. 9. 



j- Solidungula mascula mammas non habent prceterea 

 quce matribus similia sunt, Rai, Synops. method. 

 Auim. quad. &c. p. 64. 



SPINAL ACCESSORY NERVE (part 

 of the sixth pair of the older anatomists ; 

 part of the eighth pair of Willis ; nervus 

 accessorius ad par vagum; nervus accessorius 

 Wittisu ; the eleventh pair of Soemmering ; 

 the beinerve of the German anatomists). 

 This nerve is attached to, or, as it is more 

 commonly expressed, arises from, the lateral 

 surface of the cervical portion of the spinal 

 chord close to the posterior roots of the 

 spinal nerves ; and it lies between the pos- 

 terior roots of the spinal nerves and the 

 ligamentum denticulatum. On entering the 

 cranium by the foramen magnum, it continues 

 to receive additional roots or filaments of 

 origin froni the medulla oblongata. It com- 

 mences by a very slender filament, most ge- 

 nerally opposite the fifth or sixth posterior 

 roots of the spinal nerves, and in its passage 

 upwards to the interior of the cranium, its 

 bulk is gradually increased by additional fila- 

 ments of origin from the lateral surface of 

 the spinal chord and from the medulla ob- 

 longata. The filaments arising from the 

 spinal chord pass upwards and a little for- 

 ward to join the trunk of the nerve, so that 

 it lies a little nearer to the ligamentum den* 

 ticulatum than the attachments of the fila- 

 ments forming it. After it enters the cranium 

 by the foramen magnum, it runs forward, 

 outward, and upward, places itself in close 

 apposition to the posterior surface of the 

 par vagum, and escapes from the interior of 

 the cranium, through the foramen lacerum 

 posterius, along with the vagus and glosso- 

 pharyngeal nerves. The roots of the acces- 

 sory that arise from the medulla oblongata 

 are placed in the same line with the lower 

 roots or filaments of origin of the par vagum ; 

 and the upper roots of the former approach 

 so closely to the lower roots of the latter, 

 that it is frequently difficult to say with con- 

 fidence where the roots of the one nerve end 

 and those of the other begin. (Fig. 521, 3, 5.) 



Previous to the time of Willis, anatomists 

 considered this nerve as constituting a part of 

 the vagus, and to him is due the credit of 

 first pointing out clearly the grounds on 

 which its separation from the vagus rests. 

 Very great discrepancy exists in the descrip- 

 tion of the origin of this nerve given by the 

 best anatomists. This is explained, not only 

 by the fact first pointed out particularly by 

 Scarpa*, that its filaments of origin are at- 

 tached over different extents of the spinal 

 chord in different individuals, and sometimes 

 to a greater extent on one side than on the 

 other in the same individual, but also by its 

 lower roots or filaments of origin being so 

 slender that they sometimes cannot be ac- 

 curately traced by the naked eye. Willis 

 himself describes it as commencing by a very 

 slender beginning near the sixth or seventh 

 cervical nerve.f Scarpa ascertained that its 



* Abhandlung iiber den zum achten Paare der 

 Gehirnerven hinlaufenden Beinerven. In den Ab- 

 handlung der rom. K. K. Josephinischen Med. 

 Chir. Academic, Band i. Wien, 1787. 



t Cerebri Anatome, &c., Caput xxviii. p. 294. 

 Amstelodami, 1666. 



