330 



THE POPULAB EDUCATOR. 



dromedary the walls of the first and second stomachs are ex- 

 cavated into deep cells, wherein water may be retained in con- 

 siderable quantities. On this account these animals are able to 

 go many days without a fresh supply of water, even during long 

 journeys across the hot, sandy desert. The intestines (like those 

 of man) consist of two portions, of which the first is named 

 the small, and the second the large intestine. The point of 

 separation between them is indicated by a valve formed by the 

 mucous lining of the bowel, and in some animals by a caecum, 

 to which is attached a tail-like process, termed the vermiform 

 appendix. The relative length of the intestines varies. In the 

 carnivora it is from five to fifteen times the length of the body ; 

 in insectivora, from three to six times ; cheiroptera, two to 

 seven; ungulata, fifteen to thirty; in the quadrumana, about 

 three to eight times. The division into large and small intestine 

 prevails with few exceptions throughout the mammalia. The 

 membrane lining the small intestine is elevated into valvular 

 folds, for the purpose of increasing the surface over which the 

 digestive material has to pass ; there are also embedded in it 

 small glandular organs and villi ; the former secrete a fluid 

 which aids the digestive process, and the latter take into the 

 system, as white blood, that already sufficiently prepared. The 

 large intestine is sac6ulated. It commences by a blind ex- 

 tremity called the caecum, at the termination of which the small 

 intestines open. The caecum is not always present, as in the 

 insect-eaters, bats, edentata, and certain of the cetacea ; and in 

 other mammals it is variable in length. It is short in the 

 carnivora, yet absent in bears and weasels. In the ruminants it 

 is large and capacious. The appendix exists in man, apes, and 

 gibbons, and also in the marsupial wombat, but in no other 

 animal. In the monotremata (ornithorynchus) the intestinal 

 canal terminates in a cloaca, as in birds. 



The glandular organs, liver, and pancreas, and the spleen, are 

 always present. The liver has generally appended to it a gall- 

 bladder, or reservoir for the bile. In the mouth there are 

 usually three pairs of salivary glands, which furnish the secretion 

 to moisten and partially dissolve certain constituents of the 

 food This fluid readily converts starchy food into sugar, while 

 in the mouth. 



The kidneys are situated on each side the lumbar portion of 

 the spine. They eliminate the urine from the blood. This 

 excretion passes from the kidney, into the bladder by means of 

 a membranous tube called the ureter. 



The abdominal cavity is separated from the chest by a parti- 

 tion-muscle called the diaphragm. This is a very important 

 muscle, and by its contraction and relaxation the principal part 

 of the mechanism of breathing is effected. 



The lungs and heart present much the same arrangement as 

 that described in the last lesson. The lungs do not communicate 

 with air-cells in any part of the body in the mammalia, as they 

 do in birds. 



'The windpipe has surmounting it a larynx, made up of a num- 

 ber of pieces called cartilages, to which are attached numerous 

 muscles and ligaments. It is hero that the voice is produced. 



The position of the heart is usually in the median line of the 

 chest, lying between the lungs. I'i man and the higher apes it 

 has an inclination towards the left side. 



Nervous System. As will be anticipated, the brain is found 

 larger and more complicated in these animals than in the pre- 

 ceding classes. It is characterised by the presence of a trans- 

 verse band of nervous matter, which connects together the two 

 halves of which the brain is composed. This transverse band, 

 or commissure, is called the corpus callosum. It is small (said 

 to be absent) in the monotremata. The convolutions of the 

 brain are more numerous, and increase in complexity, as we 

 ascend towards the higher mammalia, according with the 

 increased intelligence which these animals manifest. The weight 

 of the brain in proportion to that of the body diminishes in the 

 vertebrata generally in the following order and manner : In 

 mammalia it is as 1 to 186 ; in birds, as 1 to 212 ; in reptiles, as 

 1 to 1,321 ; and in fishes, as 1 to 5,668 (Leuret). In proportion 

 to the body, tho brain is smaller in the larger mammals than in 

 those of less dimensions. Thus, in the ox, it is as 1 to 180 ; in 

 the elephant, as 1 to 500 ; in the horse, as 1 to 400 ; in the 

 sheep, as 1 to 350 ; in the dog, as 1 to 305 ; in the cat, as 1 ':o 

 156 ; in the rabbit, as 1 to 140 ; in the rat, as 1 to 76 ; and in 

 the field-mouse, as 1 to 31. In man, the average proportion is 

 aa 1 to 36' 5 (Marshall), With the exception of a few small 



birds, certain rodent animals, and the smallest of the monkey, 

 tribe, man has a larger brain, in proportion to the size of the 

 body, than any other vertebrate. 



Sensory Organs. We find these delicate organs developed is 

 the highest degree of perfection in this class. The pupil of the 

 eye varies in shape. In man, and many of the larger carnivora, 

 it is round. In nocturnal animals, as the cat, it assumes the 

 form of a vertical fissure, and is very largo. In many of the 

 herbivorous . animals it is transversely oblong. In the whale 

 tribe the eye is similar in shape to that already described in 

 fishes. The eye is moved by six muscles. It is protected by 

 two movable lids. Besides these, there is sometimes a third 

 lid, called the nictitating membrane. The minute structure 

 of the eye is in almost every respect similar to that of man, 

 which will be described elsewhere, as also the organ of hearing 1 . 



The nose consists of two lateral halves, the cavity being 

 divided by a vertical septum. It is invested by a delicate mem- 

 brane (mucous), in which the olfactory nerve filaments, which 

 preside over the sense of smell, ramify. Both cavities com- 

 municate with the upper part of the gullet, or pharynx. The 

 sense of smell is very acute in the majority of members of this 

 class. 



The proboscis, or trunk of the elephant, is a prolongation of 

 the nose. It consists of a highly flexible tube, surrounded with 

 muscles, through which food and water are conveyed to the 

 mouth, and air to the lungs. It also serves as an organ of pre- 

 hension. By means of its trunk the elephant is enabled to 

 uproot trees, untie knots, open a lock, or even write with a pen 

 (Rymer Jones). 



The Skeleton, in many respects, presents a close analogy to 

 that of man. It undergoes, however, many modifications. Tho 

 skull and face are formed by a series of bones immovably bound 

 together, and so arranged as to present several complete and 

 incomplete cavities for the lodgment of the delicate organs con- 

 cerned in the manifestation of the senses. Thus we have one 

 cavity, of variable size, for the brain ; another one for the nose ; 

 and one on each side of tho face for the eyes. Tho mouth is 

 situated at the base, in the interval between the upper and 

 lower jaws. The sjze of the face becomes larger, and the 

 cranium smaller, as we recede from man. The jaws are always 

 articulated to tho squamosal bone of the skull, without the 

 intervention of a quadrate bone, as in the preceding classes. 



Some of the mammalia (ruminants) have horns projecting 

 from the frontal bones. In deer tho horns are called antlers, 

 and are replaced annually. The horns of the rhinoceros are 

 mere appendages of the skin. In the goat, ox, and sheep, the 

 horns are hollow, and based upon an osseous process, which is 

 hollowed out into cells. These communicate with certain 

 cavities in the frontal bone, called sinuses. Such horns grow by 

 layers, analogous to ordinary nail, and are never shod. With 

 the exception of camels and musks, all the ruminants are pro- 

 vided with horns. 



The vertebral column is made up of bone segments. These are 

 respectively named cervical, dorsal, lumbar, sacral, and caudal, 

 according to their position. The cervical are usually seven in 

 number(Fig.XV.,12). The dorsal (13) vary from cloven to twenty, 

 and give attachment to a corresponding number of ribs. Thus, 

 in man there are twelve dorsal vertebras, and as many ribs. 

 The horse has eighteen, and the elephant twenty pairs of ribs. 

 The sacral vertebrae are absent in the whale tribe. In other 

 mammals they consist of three or more segments fused together, 

 forming a wedge-shaped bone, called the sacrum (15). The tail 

 (caudal) vertebras (16) are represented in man by four small 

 segments. In other mammals they vary to sixty in number. 

 In certain rats they are entirely absent. The weight of tho 

 head is supported by a strong elastic ligament, vulgarly termed 

 packwax, which extends between the back part of the skull and 

 the neck vertebrae. 



Every mammal is provided with four limbs, except the whalo 

 tribe, and these have only the two thoracic or anterior limbs. 

 The limbs present many peculiar modifications, according to the 

 habits and sphere of the animal. Thus, the thoracic limbs of 

 the bat act as wings ; those of the whale, as oars ; in quadrupeds 

 as legs ; and in some, as the cat tribe, also as instruments of 

 offence. In monkeys they are indiscriminately used as hands and 

 feet ; while in man the hand and arm are emblematical of his 

 skill and prowess by them he is enabled to accomplish the 

 various duties which the exigencies of life entail upon him. 



