382 _ SURG. J. C. THOMPSON ON THE 
Specimen. — U.S. National Museum No. 504006. Sausalito 
Peninsula, California. Adult female. 
The tracheal membrane begins at the glottis; anteriorly it lies 
along the dorsal and right quadrant of the tube, and further on, 
at about the 16th gastrostege, it gradually winds to the dorsal 
quadrant. Anteriorly it is narrow and the ends of the carti- 
laginous rings are in apposition; at the 6th g. it is 1 mm. wide 
and begins to be lined with alveolar tissue; where the trachea 
enters the lung the membrane is 3°D mm. wide and its alveolar 
lining becomes confluent. with the respiratory tissue of the lung. 
The air-cells on the membrane near the end are smaller than 
those lining the anterior portion of the lung. The trachea 
enters the lung at the 24th g. From without it appears to 
terminate in an obtuse angle a few millimetres posterior to the 
base of the rudimentary lung ; from within it is seen to continue | 
along the ventral surface of the lung as a narrow, straight, and 
shallow gutter of fibrous tissue which reaches nearly. to the 
anangious portion. The right lung is lined with pulmonary 
tissue to about the 40th g.; from this point on the air-cells 
become larger, more irregular, and deeper; they may be said to 
terminate, and the anangious portion to begin, at about the 45th ¢ 
From this poimt the lung continues as an air-sac to the level of 
the 106th g. 
There is a free apex: extending forward 8 mm. in relation with 
the right side of the trachea; this apex opens into the lung by a 
restricted aperture, 2°5 sam. in diameter, which is just aritenion 
to the opening in the rudimentary lung. The rudimentary left 
lung is 7 mm. long, lined with air-cells, and opens into the trachea 
at a point 4°5 mm. anterior to where the trachea terminates in 
the right lung. 
The vertebral artery vises from the right aortic arch at the level 
of the 20th gastrostege and is superficial in its course to the 
10th g. It gives off five intercostal branches: I-20; IJ.-16; 
T11.-15; 1V.-14; V.—-12; and one branch to the esophagus at 
the 14th g. The right aorta gives off a single intercostal branch 
close to its junction with the left; this branch arises at the 
29th g., courses upwards and forwards and enters at the 27th g. 
The left aorta is only a trifle larger than the right and is without 
branches. The dorsal aorta begins at the 29th g. 
There are sixty intercostals, and all but Nos. LAVAL: and LIX. 
enter in the mid-dorsal line. The gastrostege level at which 
they leave the aorta is as follows:—I.-31; I1.-35; III.—41; 
LV.-44; V.-50; VI.-53; VIL-55; VIII-—57; 1X.-60; X.-62; 
XI.-64; XIT.-66; XIIT.-68; XIV.-72; XV.-73; XVI-75; 
XVIIL-77 ; XVIII.-79; XTX.-82); XX.—84; XXI.-86; XXIT— 
88; XXIIT.-90; XXIV.-92; XXV.-93; XXVI.-95; XXVIT.— 
96; XXVITI.-99;° XXIX-101; XXX.-103; XXXI.-104; 
XXXIT.-106; XXXTIT-108; XXXIV.-110; XXXV.-111; 
RRRV I A1I2 5 XXX VAT 3) 5, ROO Ti OXOS RES 
116; XL-117; XLI-119; XLIL-121; XLISI.-122 ; XLIV.— 
