Page:The American Cyclopædia (1879) Volume XI.djvu/86

 78 MAMMALIA the epiglottis. In ordinary respiration the air passes noiselessly ; but when the will contracts <>r otherwise modifies these cords, sound is produced, which in man becomes articulate speech by the action of the pharynx, nasal pas- sages, and parts contained within the mouth. The epiglottis exists in all mammals, but it is sometimes divided at the upper end ; in ceta- ceans, the larynx ascends to the posterior nares and communicates with the blow-hole on the top of the head. The lion's roar de- pends on the great size of the larynx ; the jrrunt of the hog is produced in cavities com- municating with its ventricles; the neigh of the horse by vibration of folds connected with the vocal cords; the bray of the ass by re- verberation in a large cavity with small aper- ture under the thyroid cartilage ; in the howl- ing monkeys the hyoid bone is dilated into a large membranous sac, in which the loud sounds of these animals are produced ; in the marsupials the voice is very weak. The uri- nary system of mammals consists of secretory organs (the kidneys), and a reservoir for the secreted fluid (the bladder), communicating with the former by the ureters and externally by the urethra. The kidneys of mammals pre- sent the same external cortical and internal tubular portions as in man, and also the supra- renal capsules, in the lumbar region near the vertebra and external to the peritoneal sac ; they differ somewhat in form, being more or less lobulated, as in the human foetus, in ceta- ceans, seals, otters, bears, the elephant, and ox; the lobules vary from 10 in the otter to 130 in the seals, in cetaceans resembling a bunch of grapes ; in all, except the monotre- mata, the ureters open into the bladder ; in these into the urethra, as in cnelonians. The bladder is generally more loosely connected in other mammals than in man; it is largest in the herbivora, smaller and more muscular in the carnivora and rodents. The chemical com- podtion of the urine is about the same in car- nivoru as in man, except in the absence of uric acid ; in the herbivora it is alkaline, contain- ing hippuric acid and much earthy carbonate. In the stags, below the inner angle of the eyes, there is an opening communicating with a large membranous pouch, from the glands of vhich is secreted a brownish liquid, flowing down the sides of the face, like tears; many nimals have glands on the abdomen, in the groins, or about the genito-anal openings, whose secretion is very odorous, as in the musk deer, beaver, civet, and skunk. The special internal male organs are the testes, which se- i the sperm, with certain accessory glands (as the prostate and Cowper's), and seminal ' " r Mrfwdfl it, &e tVinalr th,- us are formed in the ovaries, whence they escape through the Fallopian tubes into the uterus, and thence when full-grown externally the name mammal imports, they have also external glands for the secretion of milk, the mamma or breasts. The testes may be per- manently external, as in the dog; always ab- dominal, as in the seal, elephant, and cetace- ans; or external during the rutting season, and at other times internal, as in the mole and porcupine. The epididymis is usually largely developed; the seminal vesicles are found in monkeys, bats, rodents, and pachyderms, but are wanting in carnivora, most plantigrades, ruminants, and marsupials ; the prostate gland exists in some form in all mammals; the ab- sence of Cowper's glands in most pachyderms, rodents, and carnivora shows that their action is not essential to reproduction. The human ovaries are two oval, glandular bodies, about an inch long, in the posterior portion of the broad ligaments ; each contains about 20 Graa- fian vesicles, enclosing an ovum. All the in- ternal organs, except the uterus, are much alike in the other mammalia. This last organ, single in the monkeys, is in carnivora, many rodents, pachyderms, ruminants, and cetaceans, generally divided at the base into two horns (cornua), each sometimes having its distinct opening ; in marsupials the ovaries are more or less racemose, as in birds. In most mam- mals, after the fecundated ovum has descend- ed through the Fallopian tube (in the higher orders about the 12th day), an intimate vas- cular connection takes place between the si- nuses of the parent and the chorion of the foatus, forming the placenta, which continues to supply the young with nutriment until it is capable of an independent existence. The period of utero-gestation, about 270 days in the human mammal, varies in the different families. This group of placental mammals has been called monodelphians to distinguish them from the didelphians, which include the marsupials and monotremata ; the former have a more perfect brain, with its hemispheres united by a corpus callosum ; the latter bring forth their young in a very imperfect condition, but have the brain destitute of a corpus callosum, the ab- dominal walls supported in front by two bones arising from the pubis, and an external pouch for the reception of the young. Prof. Jeffries Wyman (" Proceedings of the Boston Society of Natural History," vol. vi., p. 363), from the examination of a large number of foetal pigs, has shown that the above division of mammals into " placentals " and " implacentals " is not well defined; he found that in pigs there is, strictly speaking, no placenta, the maternal and foetal vessels being in relation only by means of very minute diffused villi and slight foldings of the chorion ; this condition is in- termediate between those of marsupials and ruminants, and shows such a gradual transi- tion in this respect that the former must be brought nearer than has been usually admitted to ordinary mammalia. Mammary glands ex- t in both sexes, but serve for purposes of lactation only in the female ; the number is generally in relation with the number of the young at a birth; there are 2 in monkeys,
 * i bony pouch, and each ventricle opens into