THE ANATOMY OF BIRDS. — OOLOGY. 
215 
adjuncts, are the pancreas and the liver. The former is that kind of lobulated salivary gland 
which in mammals is called the sweetbread." It lies in the duodenal loop, along which its 
loosely aggregated lobes extend. Its ducts, formed by the successive union of smaller efferent 
tubes, are two or three in number; they pierce the intestine a little below its commencement 
at the pylorus, and pour into the canal the pancreatic juice, which has the property of emul- 
sionizing fat. The liver is a well-known glandular organ of very special structure and func- 
tion, secreting the fluid called bile, also received into the intestine. It is of moderate size in 
birds, and deeply divided into two principal (right and left) lobes : in some birds there is also a 
smaller lobe ; and one of the large lobes may also be divided. The lobes dispart above to 
receive between them the apex of the heart ; they are held in place by pleuro-peritoneal folds 
contributing to form the thoracic-abdominal air-cells. The viscus receives venous blood from 
the extensive portal system of birds; two hepatic veins then conduct it to the post-caval. The 
emunctory ducts, carrying off the bile, are two or three in number. One at least goes directly 
to the intestine, and another to the gall-bladder, when that cyst exists ; in which case there is 
a separate cystic duct from the bladder to the intestine, no ductus communis choledochus, or 
duct common to the hepatic substance and its cyst, being formed in birds. Two hepatic ducts 
may coexist with a cystic duct, making three to the intestine, all separate; two is the rule 
when there is no gall-bladder. These emunctories commonly enter the intestine some distance 
apart, and after the pancreatic ducts. The gall-bladder is generally present, frequently absent ; 
it may occur or not in closely related genera of birds. 
g. Oology: the Uro-Genital Organs. 
The Urinary and Generative Organs may be conveniently considered together, not 
only on account of their close anatomical relations, but because their physiological functions, 
totally diverse in adult life, are primitively related in the most intimate manner. For it is a 
singular fact that the mean office of straining urine out of the system is at first sustained by a 
structure (wolffian body), in closest connection with which, in the female, actually as a part of 
which, in the male, are later developed those organs (ovary and testis) whose exalted office 
is creative; for these permanent genital glands procreate the microscopic creatures called 
Dt/namamoebce, the marriage of which results in the reproduction of a complex organism like 
the male or female parent. (See figs. 103, 104, and following.) 
The Wolflaan Bodies, or primordial kidneys, are a pair of tubular structures which 
appear very early in the progress of development of the embryo, beneath the spinal column, in 
front of the fore end of the future kidneys ; with each of them is developed a duct, the wolffian 
duct, which carries their excretion into the cavity of the allantois (the future cloaca). Upon 
the appearance of the true kidneys, the transitory wolffian bodies and ducts lose their urinary 
function; they ultimately disappear from the female, for the most part, leaving only a trace of 
their former existence in certain vestigial structures (parovaria, etc.) ; in the male, likewise, 
they atrophy, but not to the same extent ; for a portion of the bodies persists as an accessory 
(epididymal) portion of the testicle, and their ducts persist as the sperm-ducts, or vasa deferen- 
tia. Meanw^hile, in closest connection with the wolffian bodies, appears a pair of organs, the 
genital glands, for a while exactly alike. If the new creature is to become female, the genital 
gland develops to a certain complexity of tissue and becomes the ovarg ; while a certain duct, 
the mUllerian duct, developed coincidently to connect such ovary with the cloaca, becomes 
the oviduct. In birds usually only one ovary and oviduct (the left) becomes functional. If 
the new creature is to become male, the same genital gland develops to a higher degree of 
complexity^ acquires a tubular structure, and becomes the testicle; it connects with remains of 
the wolffian body, and the wolffian duct becomes the permanent sperm-duct, conveying the 
