462 THE EESPIEATOEY APPARATUS IN MAMMALIA. 



is less extensive, but thicker) ; 4, A hyo-epiglottidean muscle bifid at its origin. (There 

 is no aryteuo-epiglottidean ligament.) 



The trachea of these animals does not offer any important differences. The last ring is 

 not so developed as in the Horse, and the tube detaches a supplementary bronchus to a 

 lobe of the lung which does not exist in Solipeds. (The rings of the middle portion are 

 proportionally narrow, and their extremities meet behind and form a salient ridge.) 



PIG. The larynx of the Pig is remarkable for its great mobility, suspended as it is to 

 the hyoid cornua by the base of a very developed epiglottis, rather than by the wings of 

 the thyroid cartilage. u There are wide, shallow, lateral ventricles, which have a small 

 oblong sinus that ascends between the thyroid cartilage and the mucous membrane. 

 These ventricles are not surrounded by the thyro-arytenoideus muscle, which is small 

 and undivided ; above and outwardly, they are margined by a thick cord a kind of 

 superior vocal cord, considered by Duges as acting with the ventricles to modify the 

 deep grunting sounds." * (Instead of a tuberosity on the external face of the thyroid 

 cartilage, there is a median crest, and its inferior border has a small point. The cricoid 

 appears to be drawn downwards and backwards, and its lower border is very prominent in 

 the middle, and articulates with one or two small cartilaginous plates which have been 

 sometimes wrongly described as belonging to the proper cartilages of the larynx. The 

 antero-superior angles of the arytenoid cartilages are united to a small cartilaginous 

 piece which prolongs them ; their external face has a spine, and the internal angles are 

 separated by a small pisiform body called the ' interarticular cartilage.") 



The trachea of this animal resembles that of Kuminants. (It has about thirty rings, 

 and has three bronchi.) 



CARNIVOBA. The larynx of the Dog and Cat is very like that of the Horse. In 

 proportion, the epiglottis is shorter, wider at the base, and more triangular than in the 

 other species ; the lateral ventricles are shallow. (There is an interarticular cartilage as 

 in the Pig ; there is no sub-epiglottidean ventricle, and the vocal cords appear to be 

 nearer each other. The trachea has about forty-two rings, whose extremities do not meet ; 

 the space between them is less in the Cat than the Dog.) 



The larynx and trachea of Man will be compared with that of animals when we come 

 to describe the lungs. 



THE THORAX. (FigS. 230, 234.) 



The thorax, also called the thoracic or pectoral cavity, lodges not only 

 the lungs, but also the heart and the large vessels that spring from or 

 pass to that organ, with a portion of the oesophagus and trachea, as well 

 as nerves, which are as remarkable' for their number as their physiological 

 importance. 



Situation. We have seen that the thorax has for its base the bony cage 

 formed by the ribs, sternum, and bodies of the dorsal vertebrae. Suspended 

 beneath the middle portion of the spine, this cage is transformed into a 

 closed cavity by the intercostal muscles, which fill the spaces between the 

 ribs ; and by the diaphragm, that vast oblique partition which separates the 

 thorax from the abdomen. 



Internal conformation. Considered as a whole, the thoracic cavity 

 represents a hollow cone placed horizontally, depressed on each side, and 

 particularly in front towards the summit; with its base, formed by the 

 diaphragm, cut very obliquely, in consequence of the direction taken by that 

 muscle. This obliquity of the diaphragm renders the antero-posterior 

 diameter of the cavity much greater above than below ; the difference is 

 more than double. 



The internal surface of this conical cavity may be divided into six 

 regions : a superior, inferior, and two lateral planes, a base, a posterior plane, 

 and a summit. 



The superior plane presents, on the middle line, a large projection 



resulting from the union of the vertebral bodies ; and, laterally, two deep 



channels furrows the vertebro-costal channels. These latter, wider behind 



than before, are formed by the superior extremities of the costal arches ; 



1 Lavocat, ' Anatomic des Animaux Domestiques.' 



