2 TOPOGRAPHICAL ANATOMY OF THE 



muscular fibres are lost in the superficial fascia and become adherent to 

 the surface of the brachio-cephalic muscle.^ 



A cutaneous branch of the sixth cervical nerve should be noted 

 crossing the surface of and supplying filaments to the thick sternal part 

 of the cutaneous muscle. 



Dissection. — Sever the sternal attachment of the cutaneous muscle, 

 make a longitudinal incision through the muscle along the middle line of 

 the neck, and reflect it from the surface of the underlying sterno-cephalic 

 muscle. 



In cleaning the m. sternocephalicus take care to secure a small nerve 

 that runs between its lateral border and the jugular vein. It is well 

 also, early in the dissection, to find the nerve that supplies the sterno- 

 cephalic muscle. This is the ventral branch of the accessory nerve, 

 which enters the muscle a short distance before the commencement of the 

 tendon by which it is attached to the mandible. 



M. STERNOCEPHALICUS. — The sterno-cephalic ^ is an elongated 

 rounded muscle that takes origin from the manubrium of the sternum in 

 common with its fellow of the other side of the neck. The right and 

 left muscles lie alongside each other until the middle of the neck is 

 reached. Here they diverge, and each tapers to a flattened tendon that 

 passes underneath the parotid gland to be inserted into the border of 

 the ramus of the mandible. 



V. JUGULARis. — The horse has only one jugular^ vein on each side 

 of the neck, this corresponding to the external jugular of other mammals. 

 The position of the vein is clearly indicated on the surface of the body 

 by the groove bounded by the sterno-cephalic and brachio-cephalic 

 muscles. In the present dissection the vessel will be found without 

 difficulty as it follows the border of the sterno-cephalic muscle. 



The jugular vein is formed by the union of the external and internal 

 maxillary veins at the posterior ventral angle of the parotid gland. It 

 passes down the neck in the groove bounded by the adjacent borders of 

 the sterno-cephalic and brachio-cephalic muscles, and, throughout the 

 greater part of its course, is superficial in position, being covered only by 

 the skin, the thin cutaneous muscle, and the cervical fascia. On 

 approaching the entrance to the thorax, where it joins its felloiv and 

 the subclavian veins to form the cranial vena cava, it occupies a deeper 

 position. As far as the level of the fifth cervical vertebra the vein lies 

 upon the omo-hyoid muscle, which separates it from the trachea and 



1 The degree of development of the muscle varies very considerably. It may be 

 so extensive as to cover the greater part of the sterno-cephalic muscle. 



^ Sternum [L.], aripvov (sternon) [Gr.], breast or chest ; Cephalicus [L.], K€(pa\LK6s 

 (cephalicos) [Gr.], pertaining to the head (Ke(pa\7j). 



2 Jugularis [L.], pertaining to the neck (juguhim). 



