26 TOPOGRAPHICAL ANATOMY OF THE 



artery of the spinal cord. Rami imvscidares may be grouped into 

 a dorsal and a ventral set. The dorsal rami supply those muscles 

 that lie along the dorsal aspect of the vertebral column, and anasto- 

 mose with branches of the deep cervical artery. The ventral rami 

 supply the scalenus, longus colli, longus capitis, and intertransverse 

 muscles. 



The vertebral vein follows the ventral border of the artery. 



Accompanying the vertebral vessels through the transverse fora- 

 mina is a nerve formed by the union of filaments (rami communicantes) 

 from the second to the sixth spinal nerves. It joins the first thoracic 

 sympathetic ganglion. 



Dissection. — Subsequent dissection will be facilitated if the head and 

 neck be now detaclied from the rest of the body by disarticulation 

 between the fifth and sixth cervical vertebrae. 



Before any further dissection is carried out, the external ear, as it is 

 in tlie living animal, slioukl 1)8 examined. 



The external ear (Auris externa). — The freely movable auricula 

 or lyinna,^ by which sound waves are collected, has a broad base, 

 connected with the external acoustic meatus of the temporal bone, 

 resting upon a bed of adipose tissue, the presence of which is an 

 important factor in mobility. Its free extremity or apex is pointed, 

 flattened, and gently curved so as to point forwards when the opening 

 of the ear is directed lateral wards. The dorsum of the ear is markedly 

 convex where it joins the head, but becomes flattened as the apex 

 is approached. The concave surface is the counterpart of the dorsum, 

 but carries several ridges that interrupt the smoothness of the wall 

 of the cavity. The anterior boundary of the opening of the ear is 

 mainly convex, though it has a shallow concavity near the apex. The 

 lower part of this border splits into two crura lielicis. The posterior 

 border of the pinna is convex. 



Dissection. — The skin is now to be removed from the whole of the 

 ear and the parotid region, in order that the auricular muscles, vessels, 

 and nerves may be examined. But before the dissector proceeds to 

 a detailed examination of the mu.scles, it is well that he make himself 

 acquainted with the form and disposition of the cartilages to which they 

 are attached and upon wliich they act. 



The cartilages of the ear. — The cartilages of the external ear are 

 three in number — conchal, scutular, and annular. The conchal^ 

 cartilage, or cartilago auriculae, is the largest, and forms the basis 

 and determines the shape of the projecting, conspicuous part of the 

 ear of the living animal. It may be said to be funnel- like or 



' Auricula [L.], the external ear. Pinna [L.], a wing. 

 2 Concha [L.], a shell. 



