74 PROFESSOR OWEN ON THE AYE-AYE. 
more than usually extended forwards and contracted. The cricoid (2b. c) is notched at the 
middle of its broad posterior part : the thyro-cricoideal space is small. Both cricoid and 
thyroid were partially ossified, and would probably become more so in older individuals. 
The thyroid gland is represented by two separate small flattened bodies, closely attached 
to the sides of the third to the seventh tracheal rings, inclusive. The tracheal tube (7b. /), 
about 3 inches in length, is rather flattened from before backward. The rings, about 
twenty-six in number, are unclosed behind ; their free ends meet there, without over- 
lapping, and, by the elasticity of the connecting tissue, can be drawn apart. The 
bronchial tubes are more flattened, and about 5 lines in length, before entering 
the lungs. : 
The right lung (PI. XXII. fig. 3) is divided into three lobes (7d. f, g, h), with the lobulus 
impar (7.7). The latter is grooved interiorly by the great post-caval vein, or inferior vena 
cava, and extends from the pleural space to the middle of that vein. The middle lobe 
is the smallest, and lies anterior to the interspace of the other two ; it is trihedral, and, 
as it were, pendunculate, swelling out after its origin. The left lung is divided into two 
(ib. m, n) lobes, the lower being the largest, and notched near its lower end. 
The heart is rounded, subdepressed, with an obtuse apex. The arteria innominata 
gives off both carotids and the right subclavian, then the left subclavian. The aorta, 
bending over the left bronchus, takes the usual course through the thorax into the abdo- 
men. Here it gives off the gastric (PI.X XIV. fig. 1, g), the mesenteric (ib. m), and the 
renal (7b. r) arteries, which ascend obliquely to the kidneys. About an inch below the 
renal are sent off the spermatic arteries (7b. s); below these is the inferior mesenteric (7b. 2). 
One inch and a half below the renal arteries, the aorta divides into the common iliacs (/) 
and the caudal artery (¢). ‘The mesenteric artery, first describing one large arch, next 
gives off a series of smaller secondary arches, from which the branches proceed directly 
to the intestine. The artery to the mesocolon is a branch of the mesenteric. The 
mesocolic artery forms two small arches at the base of the fold of the colon, and gives off 
the vessels to the rest of that intestine, without any anastomotic arches. ‘The axillary 
artery (Pl. XXII. fig. 2, & Pl. XXIII. fig. 1, z) is continuous, from the subclavian to the 
brachial (7b. 7), as a single tube, not broken up into numerous small branches as in the 
slow Lemurs. This was the case in both the upper limbs of the Aye-aye, in which a variety 
was observed in the giving off of the ordinary branches. In the right arm, the brachial 
artery gave off the superior profunda (Pl. XXII. fig. 2, 0), the inferior profunda (wu), and 
the anastomotica magna (s), with the medullary nutrient artery and small muscular twigs. 
In the left arm, the brachial sent off the radial artery (Pl. XXIII. fig. 1, d) from about 
the middle of its course, which, after distributing a muscular branch to the biceps, 
passed over the bend of the elbow-joint to its usual position by the side of the supinator 
longus (23). In both arms the brachial artery was continued as an undivided trunk 
to the entocondyloid foramen, through which it passes along with the median nerve (m). 
The iliac artery (Pl. XXIV. fig. 1, 2), in like manner, is continued into the femoral 
