778 SENSE ORGANS AND INTEGUMENT OF THE PIG 



The caruncula lacrimalis has the form of a ridge ; it divides into two branches 

 which join the skin at the inner commissure. It is red in color and contains 

 numerous large coil glands. 



The lacrimal gland is mucous in type. There is no lacrimal sac, and the two 

 lacrimal ducts pass through separate openings at the infraorbital margin. The 

 naso-lacrimal duct is usually short and opens into the inferior meatus at the pos- 

 terior end of the inferior turbinal.^ 



The eyel)all appears small, partly on account of the narrowness of the palpebral 

 opening; it closely approaches the spherical form. The cornea, although in reality 

 almost circular, appears oval when viewed from the front, the inner end being much 

 the broader. The chorioid has no tapetum. The iris is usually dark grayish- 

 brown or yellowish-brown, but sometimes has a blue tinge. The pupil is a trans- 

 verse oval in ordinary light, but almost circular when dilated; granula are not 

 present. The optic papilla is nearer the posterior pole than in the horse and ox, 

 and has a distinct central artery and vein. 



THE EAR 



The external ear differs considerably in size, thickness, and position. It may 

 be carried vertically, inclined inward, or hang downward. It is relatively wide and 

 is little curved except at the base. The concave surface presents several cutaneous 

 ridges which correspond approximately with the long axis of the ear. The anterior 

 ])order of the concha is strongly recurved in its lower part, and divides into two 

 branches, one of which passes almost horizontally backward in the cavum conchse, 

 while the other continues the general direction of the border. The posterior border 

 is slightly concave above, strongly convex below, forming a prominence somewhat 

 analogous to the lol^ule of the human ear. The osseous external auditory meatus 

 is very long and is directed downward and inward. The tympanic membrane is 

 almost circular. 



The tympanic cavity proper is small, but it is continuous wath the numerous 

 cells of the large Ijulla ossea. The Eustachian tube is short ; its pharyngeal opening 

 is situated in the upper part of the wall of the pharynx immediately behind the 

 posterior nares. It is somewhat infundibular, and is bounded internally by a thick 

 fold of mucous membrane (Torus tubarius). 



THE SKIN AND APPENDAGES 



The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually ac- 

 cumulates in the subcutis and forms a distinct and often extremely thick panniculus 

 adiposus over the greater part of the body. 



The sebaceous glands are in general small and much fewer than in the other 

 animals. The sweat glands, on the other hand, are large, yellow or brownish in 

 color, and are in many places visible to the naked eye. At the inner side of the 

 carpus there are small cutaneous diverticula, the so-calletl carpal glands, into which 

 numerous compound coil glands open. Large glands also occur in the skin of the 

 digits and interdigital space. Compound tu])ular glands are present in the skin of 

 the snout. Large sebaceous and sweat glands are found at the entrance to the pre- 

 putial diverticulum. 



The hairs are sparsely scattered in improved breeds — indeed, in some cases 

 the skin is almost bare. The long hairs or bristles are arranged usually in groups 



' Tlie lower punctuin lacrimiile is frequently absent and the eorresponding duct therefore 

 blind. There is often a duct or its remnant which opens below the inferior turbinal fold, but is 

 not connected behind with the functional duct. 



