2 DESCRIPTIONS OF PREPARATIONS. 



lobe of the right lung placed far back and to the right, and, like the lungs 

 of all mammals, freely suspended in its pleural cavity and bearing no im- 

 pressions on its exterior from the different bony constituents of the thoracic 

 cavity ; fourthly, the vena azygos of the left side between the aorta and the 

 vertebral column, passing up to arch over the root of the left lung, and join 

 the vena cava descendens of that side ; and fifthly, the spinal cord. The com- 

 plete diaphragm, forming a dome-shaped floor, with the heart and lungs in 

 relation with its convex, and the liver, stomach, spleen, and kidney in 

 relation with its concave surface, is eminently characteristic of Mammalia, 

 that of the Crocodilina alone approaching this grade of development. The 

 upper part of the pericardial sac has been removed, and the two ventricles 

 (less distinctly separated from each other than in many mammals) and the left 

 auricle are brought into view. The anterior surface of the heart is more 

 equally shared in by the two ventricles than is the case in many mammals, 

 in which the right ventricle forms nearly the entire anterior aspect of the 

 organ. The left vena cava descendens, a trunk which is found in most 

 Rodents, except the Guinea Pig and Agouti, is seen to pass in front of the 

 root of the left lung in company with the phrenic nerve round to the back 

 of the heart to end in the right auricle. The vena azygos of the left side is 

 seen to join it just above the root of the left lung, and at a point some way 

 above this, the vein from the fore-leg, which is in relation with the nerves 

 going to that limb, is seen passing up to join another vein, which, from its 

 being placed superficially to the sternomastoid muscle, we know to be the 

 homologue of the external jugular of anthropotomy. The external jugular 

 is the main trunk by which the blood from the interior of the skull returns 

 to the heart in the Rodents and many of the lower Mammalia, and by its 

 confluence with the vein from the anterior limb the vena cava descendens is 

 constituted. Internally to the external jugular, just above its confluence 

 with the subclavian vein, is seen a part of the hibernating gland ; externally 

 to it lies the submaxillary ; above this again we see the parotid with its 

 duct ; and above the parotid, the facial portion of the lacrymal gland 

 sending up a duct, under which a piece of blue paper is placed, to enter the 

 orbit and join there with the duct of a second portion of the lacrymal gland, 

 which is placed within the orbit, and anteriorly to the duct of the extra- 

 orbitally-placed portion. Within the orbit we see the Harderian gland in 

 relation with the third eyelid 1 . 



1 For a fuller description of these glands, see Description of Plate I, which represents a dissection 

 somewhat different from that which we have of these organs in this preparation. The lacrymal 

 gland is somewhat similarly bilobed in the human subject, consisting of a palpebral and an orbital 

 part. See Hirschfeld et Leveille, Neurologic, 1853, PI. 76, fig. 4. In man however there are 

 between twelve and fourteen minute lacrymal ducts instead of a single one as here. But the macro- 

 scopic Harderian gland and duct of the Rodentia and mammals lower than Primates except the 

 Chiroptera do not similarly represent the minute Meibomian glands with separate ducts on the free 

 edge of the eyelids ; for both sets of glands coexist in Rodentia. 



