38d 



ANGIOLOGY. 



ing proportions. Red corpuscles vary in shape, but in all 

 mammals are more or less discoid, the camelidae excepted, where 

 they are oval ; in birds, reptiles, and fishes, they are oval, and 

 also nucleated. Their average diameter in the horse, ox, or 

 sheep is about ^j^j^-^ih. part of an inch, their average thickness 

 being about one-fourth of this. Each surface is depressed 

 towards its centre, hence the corpuscle is appropriately described 

 as a bi-concave disc. 



The ivliite corpuscles are larger than the red, round in shape, 

 and nucleated. Occurring also in lymph they are sometimes 

 termed lymph-corpuscles. 



The liquor sanguinis is pale and clear, and consists of water, 

 fibrin, albumen, fatty compounds, extracts, odoriferous and saline 

 matters. The serum is a thin, transparent liquid, of a pale- 

 straw or yellow colour, consisting of the liquor sanguinis deprived 

 of fibrin. -It contains nearly 90 per cent, of water, is always 

 slightly alkaline, and coagulates when heated, owing to the large 

 quantity of albumen it contains. Fibrin is a white, stringy, 

 elastic substance, which, when the blood is in circulation, is in 

 solution, and cannot be distinguished from the other constituents 

 of the plasma. 



HEART. 



The heart is a hollow, ipvoluntary muscular organ, situated 

 between the layers of the middle mediastinum, and in the peri- 

 cardial sac, to a reflection of which it owes its external smooth, 

 glistening aspect. Its form is that of a blunt cone, slightl}^ 

 flattened from side to side, and it presents a base and an apex. 

 The foraier is turned upwu^ds, a^i to\.ards the dorsal veivebrte, 

 from which the heart is suspended by the blood-vessels that 

 spring from it; the apex points downwards, backwards, and to 

 the left side, lying at about the level of the last bone of the 

 sternum ; the organ extends from about the third to the sixth 

 rib inclusive. The average weight of the horse's heart is about 

 six pounds and a-half, its length from base to apex about eight 

 inches, its antero-posterior diameter rather less, and its lateral 

 diameter less still. 



The heart is divided by a longitudinal septum into a right 

 and left, or anterior and posterior side. Each of these is again 

 subdivided by a transverse septum into two compartments, which 

 commimicate. Thus there are four cardiac cavities, the superior 

 ones, whose free extremities somewhat resemble the ears of a 



