THE SYSTEMATIC ANATOMY OF A FCETAL SEA-LEOPARD. 227 



this a small portion of the middle lobe, whilst none of the lower lobe is visible ; 

 both lobes of the left lung show, the anterior edges and portions of the lateral 

 surfaces being seen. In the neck region the larynx and trachea form prominent 

 features, whilst at the sides of the trachea the lateral lobes of the thyroid gland 

 with the lower parathyroids are to be seen ; no thyroid isthmus is, however, to be 

 detected, a point which is noteworthy. 



The abdominal viscera from the ventral aspect (PL XIX. fig. 2) : — The liver 

 forms the most prominent organ in the abdomen, its right and left lobes, together 

 with certain accessory lobes, occupying about one-half the available space ; the right 

 lobe appears to be larger than the left, but in reality this is not the case, since, when 

 viewed from the dorsal aspect (see PI. XXI. fig. 5), the left lobe is seen to be much 

 the bulkier of the two. A fissure passes obliquely downwards and inwards from the 

 middle of the lateral aspect of the right lobe, and effects a partial subdivision of this 

 lobe into two, but the cleft does not extend deeply into its substance ; whilst a 

 small flap of the upper of the two subdivisions is seen a short distance internal to 

 the right lateral margin, and partly conceals an aperture in the lobe in which the 

 fundus of the gall-bladder appears (PI. XIX. fig. 2 15 ). 



Between the right and left lobes there is a fairly wide cleft, in which may be seen the 

 umbilical vein passing from the umbilicus towards the ductus venosus. 



Coils of small intestine are seen lying caudal to the liver, but the stomach is not 

 visible, being largely hidden by the left hepatic lobe. 



The urinary bladder is a very elongated structure, and is attached ventrally to 

 the umbilicus : it opens caudally into the cloaca. The umbilical arteries pass along 

 the lateral aspects of the viscus towards their destination in the placenta, and are 

 well seen in transverse sections. (See PI. XXI. fig. 4.) 



The chief points of interest in connection with the above description of the 

 ventral aspect of the viscera are : — 



(i.) The relative size of the thymus, which, although as a rule large at this stage 

 of development, appears in the present case to be markedly so ; the left 

 lateral deviation of its caudal extremity is also a point worthy of note. 

 The presence of isolated lobules of this gland suggests a possible origin of 

 these from some of the higher branchial clefts. 



(ii.) The deep notching of the auricular appendices in the heart is a feature which 

 seems very striking upon opening the pericardial cavity. One other point 

 also, viz. the well-marked interventricular furrow, is a characteristic which 

 becomes more marked as development proceeds, the external subdivision of 

 the ventricular portion of the heart giving it in the full-grown seal an 

 almost bifid appearance. 



(iii.) The great longitudinal extent of the liver, an organ occupying at this stage of 

 development a relatively large proportion of the abdominal cavity. 



