174 PHYSIOLOGY AT THE FAHM. 



behind. It follows from this mode of articulation that the 

 jaw-bone of the dog has little other motion than that of a 

 simple hinge, or even approaches to that of a pair of scissors. 

 The zygomatic arch formed by the junction of the upper 

 jaw-bone and the temporal bones, beneath which the largely- 

 developed temporal muscle descends, and from which the zygo- 

 matics take their origin, is very much more expanded in every 

 way than in the horse, ox, and sheep. 



Pharynx. The pharynx in the dog, as in mammals in 

 general, has a sac-like form. It is, in short, the funnel- 

 shaped commencement of the alimentary canal. It is com- 

 posed of muscular fibres of .considerable power, which are 

 fixed to the adjacent bones, and is lined by the mucous mem- 

 brane in its passage from the mouth to the gullet. Anteriorly 

 it communicates with the mouth across the orifice of the larynx, 

 and its upper part is on the level of the openings into the pos- 

 terior nostrils and the communications with the ear on each 

 side termed the Eustachian tubes. It may be described as 

 suspended beneath the base of the skull. When the muscular 

 fibres contract, the whole cavity is narrowed. 



Gullet. The oesophagus or gullet is the second part of the 

 alimentary canal, continued backwards from the pharynx in the 

 form of a tube of smaller diameter. It is the narrowest part of 

 the whole alimentary canal or primes vice. It is also the most 

 powerfully muscular. It passes through the chest united to 

 the vertebral bones of the spine, and gets into the abdomen 

 by going between the pillars of the midriff or diaphragm. It 

 is not so long proportionally in the dog as in the horse, ox, 

 and sheep. It is, however, more extensible in the dog, as in 

 carnivorous animals generally, than in the herbivorous. In the 

 dog the muscular fibres are in two layers, which are spiral, the 

 external fibres being directed from before backwards, while the 

 internal run in an opposite direction from behind forwards a 



