HEAD AND NECK OF THE HORSE 11 



glands or endocrine organs, the thyroid ^ consists of two smooth, oval, 

 reddish-brown lateral lobes, connected ventral to the trachea by an 

 isthmus, which, in the adult horse, may be represented by a fibrous 

 band only. The lateral lobes lie upon the first three or four tracheal 

 cartilages, to which they are loosely attached, and are covered super- 

 ficially by the caudal angle of the parotid gland and the sterno-cephalic 

 and omo-hyoid muscles. 



If an incision be made into the gland, the interior will be found to 

 consist of granular tissue (composed of microscopic closed vesicles) from 

 which a jelly-like colloid may be expressed. Surrounding the gland is 

 a thin fibrous capsule. 



It should be observed that, though the thyroid gland is not of large 

 size, it is very richly supplied with blood by the thyroid artery. 



The cranial cervical lymph glands are associated with the thyroid. 

 Occasionally small masses of true thyroid tissue (accessory thyroids) may 

 be found In the neighbourhood of the thyroid proper ; and there is 

 generally at least one small pale parathyroid either about the dorsal 

 border of the lateral lobe or embedded in its deep face. 



Dissection. — Tlie dissector slioukl now turn his attention to the 

 elongated triangular interval bounded by the two halves of the mandible 

 and a transverse line between the posterior border of the rami of this 

 bone. 



Begin the dissection by following the cutaneous nerves derived from 

 the second cervical nerve. Then clean up a group of lymph glands that 

 will be readily discovered in a groove formed by the muscles clothing the 

 medial surface of the mandible and others attached to the hyoid bone. 



The superficial nerves are twigs of the n. cutaneus colli, a branch of 

 the second cervical, previously encountered during the dissection of the 

 neck. They are generally two in number and follow the course of the 

 external maxillary vein, with terminal filaments that can be traced as 

 far as the symphysis of the mandible. 



M. CUTANEUS. — Though the cutaneous muscle is readily demon- 

 strated near the border of the mandible and over the parotid gland, it is 

 so reduced nearer the middle line as to be practically absent. 



The submaxillary lymph glands (lymphoglandulte submaxillares) 



are grouped into an elongated mass, which occupies the groove bounded 



laterally by the digastric and pterygoid muscles and medially by the 



omo-hyoid, sterno-hyoid, and mylo-hyoid muscles. The right and left 



groups converge and become confiuent in front. Superficially the glands 



are only covered by skin and a thin layer of fascia and cutaneous 



muscle. 



iGupeos (thyreos) [Gr.], shield, dSos (eidos) [Gr.], form. From the shield-like 

 shape of the gland in the human subject. 



