DESCRIPTION OF THE PLATES'. 



PLATE I. 

 COMMON RAT (Mus decumanus), 



Dissected so as to show, superiorly, the cerebrospinal nervous system lodged in the cranio- 

 spinal cavity, and, inferiorly, portions of most of the organs of vegetative life. 



CHARACTERS distinctive of Mammalia shown in this figure are the 

 following : the epidermic exo-skeleton in the form of hairs ; the suspension 

 of the lungs freely in closed ' pleural ' sacs ; the perfect diaphragm (c] sepa- 

 rating the cavities of the thorax and abdomen ; the smooth external 

 surface of the kidney ; the single aorta crossing the left bronchus ; and the 

 presence of an omentum or epiploon (w). 



The scalpriform incisors characteristic of the order Rodentia are con- 

 cealed in this profile view by the lips, but the figure shows well the great 

 size of the masseter muscle which is crossed by the duct of the parotid 

 gland (/) and by the facial nerve. The great size of the organs of special 

 sense relatively to the entire bulk of the animal, and of the hind limbs 

 relatively to the fore limbs, are characteristic, though not universally nor 

 exclusively, of Rodents. 



Points of less classificatory importance are furnished to us by the 

 presence of a vena cava descendens on the left side ; of smooth cerebral 

 hemispheres (Ji) ; of a uterus all but completely bifid (y and j/); of a Har- 

 derian gland (/) ; of a hibernating gland (k] ; and of a double lacrymal 

 gland (g and g'\ 



The left halves of the parietes of the craniospinal, thoracic, abdominal, 

 and pelvic cavities have been removed to expose the parts shown in this 

 figure. The integument has been removed from the greater part of the 

 facial region, but a narrow strip has been left connecting the concha of the 



1 Plates I, VI, VIII, and X, are taken from the specimens described in the first part of this 

 work. Plates II, III, XI, XII, and XIII, are from specimens of the same animals as described in 

 the first part, but prepared differently, and therefore often displaying new points. In describing 

 these Plates repetition is avoided as much as possible. Plates IV, V, VII, IX, and XIV, 

 relate to animals or groups not described before. The descriptions of these Plates are therefore 

 supplementary to the descriptions of specimens in the first part. 



