148 DISSECTION OF THE DOG 



The lingual vein appears in the angle formed by the borders of the mylo- 

 hyoid and digastric muscles, and is at once joined by a transverse vessel which 

 passes across from one lingual vein to the other. 



A group of lymph-glands (lympho-glandulse submaxillares) are present 

 about the point of junction of the facial vein and the common trunk of the 

 lingual and sublingual veins. 



V. maxillaris interna. — The internal maxillary vein is formed under 

 cover of the parotid gland, and is only visible, at the present stage of the 

 dissection, as it runs along the aboral border of the submaxillary gland to unite 

 with the external maxillary vein. 



Dissection. — Cut across the sterno-cephalic muscle a little distance from 

 its sternal attachment and turn it aside. This will permit of the demon- 

 stration of the common carotid artery, the internal jugular vein, the 

 vagus and sympathetic nerves, as well as certain muscles. 



M. sterno-hyoideus. — The sterno-liyoid muscles of opposite sides of the 

 neck lie in contact with each other in the middle line. Each takes origin from 

 the manubrium of the sternum and is inserted into the body of the hyoid bone. 



M. STERNO-THYREOIDEUS. — In the region of the sternum the sterno-thyroid 

 muscle is almost completely covered by the preceding ; but, owing to a diver- 

 gence of the two sterno-thyroid muscles they are exposed more and more in 

 their course to the larynx. 



The sterno-thyroid muscle has origin from the manubrium of the sternum 

 and from the first costal cartilage, and is inserted into the aboral border of 

 the thyroid cartilage about its middle. 



It should be noted that, a short distance from their origins, the above 

 muscles are crossed transversely by a tendinous intersection ; and that at this 

 line the two muscles of the same side of the neck are intimately connected 

 with each other. 



The nerve supply of the sterno-hyoid and sterno-thyroid muscles is largely 

 from the ventral division of the first cervical nerve ; but with this the descending 

 branch of the hypoglossal nerve is blended. The composite nerve will be found 

 along the lateral border of the muscles. 



V. jugularis interna. — The internal jugular vein is a vessel of small and 

 variable size lying, in the main, lateral to the common carotid artery. Not 

 only does the size of the vein vary in different animals, but the two vessels of 

 the same animal are not necessarily of the same calibre. The origin of the 

 internal jugular may be traced to the occipital and cerebral veins. 



Accompanying the common carotid artery, the vein is close to the trachea 

 on the right side of the neck, and to the oesophagus on the left. It ends by 

 joining either the innominate vein or the external jugular of its own side. 

 The internal jugular receives the cranial and caudal thyroid, muscular, tracheal, 

 and oesophageal veins. 



