LARUS AEGENTATUS, HERRING GULL. 631 



equal portions by a crescentic fold or reduplication of mucous membrane. The anterior 

 or internal of tliis is tbe cloaca proper, and is greatly tbo largest ; the posterior or ex- 

 ternal forms the "bursa Fahricii," and consists merely of a bulginp; or unequal dilation 

 of that portion of the cloacal parietes that is beyond the curved iold of mucous mem- 

 brane already mentioned. Just beside this fold, about a fourth of an inch on either 

 side of the median line, on the posterior aspect of the cloaca, are tvvn small papilliB, 

 placed side by side and in close contact. On the summits of these papilla) terminate 

 the ureters and vasa deferentia, the excretory ducts of the sexual and urinary orgaua. 



The pancreas occupies the whole length of the concavity of the duodenal fold. It is 

 therefore of an elongated shape, and is somewhat triangular on a cross-section. The 

 rounded free extremity of the gland is rather larger than the other end, the whole 

 organ being somewhat club-shaped. Its long slender duct opens into the duodenum 

 between the hepatic and cystic ducts. The two lobes of the liver are of very uneijual 

 size, the right being much the largest. It measures about three inches in length, while 

 the left is only a little over two. Their internal or apposing surfaces are flat, and in 

 contact for the greater part of their length, only separating ahovo to admit the apex of 

 the heart between' them. They are both somewhat of a triangular shape on a cross- 

 section ; rising up high, and thick in the middle; tapering toward both extremities; 

 the right being the most elongated and attenuated. They are somewhat loosely con- 

 *neoted by a thin, flat band of hepatic substance. The surface of both presents several 

 eminences and depressions, produced by the impact of neighboring 'organs and parts. 



The hepatic duct proceeds from the middle of the under surface of the left lobe, near 

 the commissure ; has a length of about two inches, and opens into the duodenum, as 

 already described. 



The gall-bladder lies in a depression on the under surface of the right lobe, and is 

 ■well developed. It is of an ovoid shape, tapering toward its proximal extremity ; 

 more obtuse at its distal. The cyst-hepatic duct is very short, opening directly into the 

 base of the bladder. The cystic duct arises about midway between the two extremi- 

 ties of the hlad(3er, on its posterior aspect. It is larger, but shorter than the hepatic 

 duct, and opens into the duodenum an inch further down. 



The kidneys measure about two and a fourth inches in total length, but are of very 

 varying breadth at different points along their extent. They are irregularly divided 

 into several lobes, which are not, however, of regular shape, and closely adapted to 

 each other, as in Sterna ; nor do they appear to be constant as to their mode of subdi- 

 vision. The upper lobe of each is the largest, and has the most convex outline. The 

 next is very narrow, serving as a connection between the anterior and posterior ex- 

 tremities, and is sometimes almost divided into two. The posterior lobe is nearly rect- 

 angular in shape ; about twice as long as broad ; and has a deep, longitudinal sulcus 

 upon its surface, in which is received the ureter. 



The sexual organs lie superimposed upon the superior lobes of the kidneys, closely 

 bound down to them. Their efferent ducts run along in close apposition with the 

 ureters, and terminate in the cloa'ca side by side with the orifices of the urinary ducts, 

 as has been already described. 



The superior larynx is composed of four principal elements : A thyroid cartilage, two 

 arytenoid, and a cricoid, the latter dividqd into three separate portions. The thyroid 

 is much the largest of these, forming all of the anterior or inferior portion of the organ. 

 It is of a tapering, subconical form, with an ovoid truncated extremitj', and an obtuse 

 tip. Its lateral edges curl over upward, especially posteriorly, where it supports the 

 cricoid, forming all of the cartilaginous lateral parietes which the laryux possesses. 

 Its inferior surface is marked with a longitudinal groove ; its internal with a well-de- 

 veloped eminence, situate on the median line, not distantly resembling the crista galli 

 of the human ethmoid bone. Anteriorly the thyroid extends forward as a mere flat 

 lamina, with scarcely any convexity. The posterior portions of the thyroiii support 

 the two lateral elements of the cricoid. These are quite broad at their base ; curl over 

 toward the median line ; growing narrower as they approach each other, till they com- 

 plete the circle of the larynx posteriorly by uniting with the central azygoid element. 

 This IS a small, irregular, cartilaginous nodule, situate on the median line, having, pos- 

 teriorly, two surfaces for the reception of the lateral cricoid elements ; more anteriorly 

 two others for the articulation of the two arytenoid cartilages. These latter are of 

 denser consistency than the rest of the larynx, being sometimes almost osseous. They 

 are four-tenths of an inch long. Their base presents on their inner surfaces the facet 

 for the articulation with the azygos element of the cricoid. They are so twisted or 

 curled upon their own axes, that their lateral edges, at tirst horizontal, are afterward 

 perpendicular, rising above the level of the rest of the larynx, and lying paraliel to 

 each other, thus forming the rima glottidis. These several cartilagMoiis pieces of the 

 larynx are all connected by a delicate, elastic, fibro-cellular tissue. The motion which 

 they possess is limited almost entirely to the opening and shutting of the arytenoid 

 cartilages, effected by the muscles attached to them ; the motion being chiefly at the 

 aryteno- cricoid articulation. These proper muscles of the larynx are the thyro-ary- 



