DISSECTION OF THE DOG 163 



A better opportunity for examining the hyoid attachment will be afforded 

 at a later stage of the dissection. 



M. hyo-glossus. — The hyo-glossal muscle is flat, and lies on the side 

 of the base of the tongue, lateral to the genio-glossal and genio-hyoid muscles. 

 Arising from the lateral surface of the thyro-hyal and the end of the body of 

 the hyoid bone, its fibres run dorsal wards and towards the tip of the tongue, 

 medial to those of the stylo-glossal muscle. 



M. genio-hyoideus. — The genio-hyoid muscle has its origin in the neigh- 

 bourhood of the symphysis of the mandible, and its fibres run longitudinally 

 to the body of the hyoid bone, into which they are inserted. 



M. thyreo-hyoideus. — The thyro-hyoid muscle springs from the thyro- 

 hyal bone and is inserted to an oblique line on the lateral surface of the lamina 

 of the thyroid cartilage. 



N. lingualis. — Since it is the largest branch, the lingual may be regarded 

 as one of the terminals of the mandibular nerve. ■ Its fibres reach the mucous 

 membrane of the tongue by crossing the pterygoid muscles in the first place, and 

 then the stylo-glossal muscle, the submaxillary and major sublingual ducts, 

 and the oral portion of the sublingual gland. Laterally the nerve is covered 

 by the mylo-hyoid muscle. 



N. hypoglossus. — After leaving the cranium by the hypoglossal foramen, 

 the hypoglossal or twelfth cerebral nerve is connected for a distance with the 

 accessory nerve. Medial to the origin of the digastric muscle, it crosses the 

 external carotid artery laterally and comes into contact with the lingual 

 artery. The nerve and the artery travel together as far as the border of the 

 hyo-glossal muscle, where they part company for a time ; the nerve continuing 

 lateral to the muscle, the artery disappearing medial to it. Having passed 

 the muscle, the two structures (as well as the lingual vein) once again come 

 together and travel side by side towards the tip of the tongue. 



The following are the branches of the hypoglossal nerve : (1) Filaments 

 connecting the nerve with the pharyngeal plexus, the cranial cervical sympathetic 

 ganglion, the plexus nodosus, and the pharyngeal branch of the vagus nerve ; 



(2) a descending branch (ramus descendens) leaving the parent nerve immediately 

 it has crossed the external carotid artery, to run obliquely over the pharynx 

 and larynx and join the ventral branch of the first cervical nerve. Filaments 

 are contributed to the thyro-hyoid, sterno-hyoid, and sterno-thyroid muscles ; 



(3) terminal branches of the hypoglossal nerve supply all the muscles of the 

 tongue. 



A. carotis communis. — The common carotid artery terminates on a level 

 with the thyroid cartilage by dividing into three vessels of unequal size, 

 namely, the occipital, the internal carotid, and external carotid arteries. The 

 occipital and internal carotid arteries are much smaller than the external 

 carotid, which, from its size and the direction it takes during the first part of 

 its course, appears to be the direct continuation of the common carotid. 



M 2 



