MAMMALIA. 
vena cava: they never anastomose with the me- 
senteric veins. 
The kidneys are relatively smaller, and 
present a more compact figure than in the 
other vertebrate classes; their parenchyma 
is divided into a cortical and medullary por- 
tion, and the secerning tubuli terminate in 
a dilatation of the excretory duct called the 
elvis. The tbuli uriniferi are — slightly 
ranched, and the ramification takes place in 
the dichotomous, and not pinnatifid manner: 
they are convoluted in the cortical, and straight 
in the medullary portions of the kidney, and 
with a few exceptions terminate upon valvular 
prominences, called mammille. The vreters 
convey the urine toa urinary bladder situated 
anterior to the rectum, and to the genital tubes 
or cavities. The liver is generally divided into 
a greater number of lobes than in birds. The 
portal system is formed by veins derived ex- 
clusively from the spleen and chylopoietic 
viscera. The cystic duct, when it exists, 
always joins the hepatic, and does not enter 
the duodenum separately. The pancreatic duct 
is commonly single. 
The mouth is closed by soft flexible mus- 
cular lips. The upper jaw is composed of 
palatine, maxillary, and intermaxillary bones, 
and is fixed ; the lower jaw consists of two 
rami, which are simple, or formed by one 
bony piece, and are articulated by a convex or 
flat condyle to the base of the zygomatic pro- 
cess, and not to the tympanic element of the 
temporal bone; the base of the coronoid pro- 
cess generally extends along the space between 
the condyloid and the alveolar processes. The 
jaws of Mammals, with few exceptions, are 
provided with teeth, which are arranged in a 
single row; they are always lodged in sockets, 
and never anchylosed with the substance of 
the jaw; in most cases they present dif- 
ferent forms in the same individual, and the 
molars have two or more fangs. Never more 
than two teeth succeed each other in the ver- 
tical direction, and in this case the fang of the 
deciduous tooth is always completed before it is 
shed. The tongue is fleshy, well developed, 
with the apex more or less free. The posterior 
nares are protected by a soft palate, and the 
larynx by an epiglottis ; the rings of the trachea 
are generally cartilaginous and incomplete be- 
hind : there is no inferior larynx. The cso- 
phagus is continued without partial dilatations 
to the stomach, which varies in its structure 
according to the nature of the food, or the 
quantity of nutriment to be extracted therefrom. 
An epiploon of greater or less extent is conti- 
nued from the great curvature of the stomach. 
The termination of the duodenum is generally 
tied closely to the apo’ above the root of the 
mesentery. The colon is suspended generally 
by a distinct duplicature of peritoneum, called 
the meso-colon : the cacum coli when present is 
usually single. The rectum commonly termi- 
nates by an aperture distinct from that of the 
urinary or genital canals. 
The female generative organs consist of two 
ovaries, which with very few exceptions are 
equally developed ; there are always two ovi- 
235 
duets or Fallopian tubes, a simple or more or 
less completely bifid uterus, a vagina, which 
is commonly single, and a clitoris. The es- 
sential element of the ovum, the germinal vesi- 
cle, acquires a surrounding granu} stratum 
(tunica granulosa), a small vitelline mass, and 
a vitelline membrane, before it quits the ovisac. 
The ovisacs or Graafian vesicles, consisting of 
an ovarian vesicle and a vascular layer of the 
condensed cellular tissue, or stroma of the ovary, 
are never pendent, and rarely racemose. 
The male organs consist of two equally de- 
veloped testes, commonly situated in an ex- 
ternal tegumentary pouch or scrotum : the vasa 
deferentia form an epididymis at their com- 
mencement, and frequently communicate with 
the ducts of vesicule seminales at their termi- 
nation, and the semen is conveyed outwardly 
along a complete urethral canal, where it is 
mingled with the secretion of certain accessory 
glands, of which those called “ Cowperian,” or 
‘¢ preprostatic,” are constant ; there are also ge- 
nerally prostatic and in many cases vesicular 
glands. The penis is always perforated by an 
urethral canal, along which, with very few ex- 
ceptions, the urine as well as the semen is con- 
ducted from the body. 
The true vertebre of Mammalia have their 
bodies ossified from three centres, and present 
for a longer or shorter period of life a com- 
pressed epiphysis at each extremity. They are 
articulated by concentric ligaments with inter- 
posed glairy fluid, forming what are called the 
intervertebral substances ; the articulating sur- 
faces are generally flattened, but sometimes, as 
in the neck of certain Ruminants, they are 
concave at one end and convex at the other; 
such a vertebra, however, may be distinguished 
from a vertebra of a Reptile, with a similar 
ball-and-socket structure of the articular sur- 
faces, even when found in a fossil state, and 
when the test of the articulating medium can- 
not be applied, by the constant anchylosis or 
confluence of the annular with the central part 
orbody. The cervical vertebre, with one or 
two exceptions, are seven in number, neither 
more nor less ; the Monotremes, which are the 
instances commonly opposed to other generaliza- 
tions, form no exception to this rule. The 
lumbar vertebre are more constant and more 
numerous than in other classes of vertebrate 
animals. The atlas is articulated by concave 
articular processes to two convex condyles, 
which are developed from the ex-occipital ele- 
ments of the last cranial vertebra. The tym- 
panic element of the temporal bone is re- 
stricted in function to a subserviency to the 
organ of hearing, and never enters into the 
articulation of the lower jaw. The frontal 
bones are developed each from a single centre ; 
there are no anterior or posterior frontals. The 
olfactory nerves escape from the cranial cavity 
through numerous foramina of a cribriform 
plate. The optic foramina are always distinct 
from one a and generally from the fis- 
sure lacere anteriores, and consequently give 
passage only to the optic nerves and ophthalmic 
arteries. The carotid canals do not intercom- 
municate. The cranial bones, in regard to the 
