4 INTRODUCTION. 



a series of tubes, by which the blood passes through the body, 



both systems being supplied with many accessory organs. 



In the higher invertebrate animal we find no backbone, no 

 neural canal, and no cerebro-spinal system of nerves ; but t' e 

 visceral canal exists, and its contents correspond mostly with the 

 structures found in the vertebrate. (See Fig. 1.) The lowest 

 vertebrate animals known — the Lancelot, or A'>niohioxus, and the 

 Lamprey — have no vertebral column, but they possess throughout 

 Hfe a soft, gelatinous structure, the notochord, from which, in the 

 higher vertebrates, the column becomes early developed. These 

 may be regarded as exceptional or undeveloped forms. 



If we eliminate from the Vertebrata all the classes but the two 

 highest — the Mamimalta and Aves — we shall further localise our 

 subject, since these two classes contain all the animals which, as 

 a rule, engage the attention of the veterinary anatomist, to whom 

 the first of the two is of by far the greater importance. 

 DOMESTICATED MAMMALS. 



It is sufficient to state that the Mammalia are .characterised 

 by the females being provided with an apparatus which supplies 

 milk for the nourishment of their young after birth. 



The horse, ass, ox. sheep, goat, camel, llama, pig, elephant, dog, 

 cat, and rabbit are the mammalian vertebrates, usually included 

 in the term "domesticated animals." The first eight of these 

 belong to one of the most important of the natural orders, the 

 Ungulata, or hoofed animals. The camel, llama, and elephant, 

 not being domesticated, in the proper sense of the word, in 

 Europe, the scope of the present work will not permit separate 

 sections to be devoted to their description. 



UNGULATA. 



The Ungulata which included the hoofed quadrupeds, is a 

 very large and important order, divided into two parts. One 

 section, the Perissod,acUjla, includes the animals having an odd 

 number of toes or digits ; the other, the ArtiodadyJa, contain- 

 ing those with an even number. 



PERISSODAOTYLX. 



Equidm or Solidungula. — The horse and ass are referred, in the 

 section Perissodactyla. to this family, which includes only the 

 two genera Equus and Asinus : their most prominent external 

 feature is the possession of only one perfect digit or finger on each 

 extremity. Apparently there is but one cleariy defined species in 

 the genus Equus, the features presented by the varieries which are 



