200 PROF. T. H. HUXLEY ON MENOBRANCHUS. [Mar. 17, 



chondrifications of the capsule of the olfactory sac, like those which 

 certainly take place in the case of the eye and of the ear, and that 

 the appearance of outgrowth from the trabecule is simply due to the 

 fact that this independent process of chondrification begins in con- 

 tiguity with the trabecula and extends outwards, I do not know 

 that there is any means of deciding the question at present. 



No doubt the perfect independence of the sclerotic and of the 

 wall of the primitive auditory sac, lends countenance to the hypo- 

 thesis that the olfactory sacs are provided with similar proper walls. 

 And it is easy to imagine that the antorbital process and the 

 ethmoidal alae, taken together, may represent the sclerotic and the 

 periotic cartilages ; but it is very difficult to find proof of the fact, 

 and, until such proof is produced, it may be better to enumerate the 

 auditory capsules, alone, among the paraneural elements of the skull. 



II. The Heart. 



The heart of Menobranchus has been described by Mayer and by 

 Van der Hoeven in the works already cited. 



According to the former writer (/. c. p. 83), 



" The heart is shaped like that of Proteus anguinus, and lies free 

 in the pericardium. It consists of a ventricle and an auricle with 

 two appendices (Herzohren), one on each side. The truncus arte- 

 riosus arises, as in the Batrachians, from the right corner of the 

 ventricle. Upon each side, a saccus venosus appears beneath the 

 appendix of the auricle of its side, and receives the corresponding 

 superior vena cava. But in the pericardial chamber there are two 

 inferior cava?, formed by the division of the main trunk, which enters 

 the pericardium at the upper edge of the liver. The right saccus 

 venosus finally opens into the left ; and out of this an aperture leads 

 into the simple auricle, which, however, as has been said, presents 

 two appendices. 



"Near the sinu-auricular aperiure the auriculo-ventricular opening 

 {ostium venosum) leads into the ventricle. There are two auriculo- 

 ventricular valves, with an interposed cleft. The ventricle is simple, 

 but partially divided above by a median projection of its fleshy wall. 

 The bulbus aortce gives off two branches on each side ; these pass 

 towards the branchial arches ; and the posterior again divides. The 

 three branchial arteries thus produced run along the anterior edges of 

 the branchial arches to the branchial plumes ; from these the 

 branchial veins pass along the posterior edges of the branchial 

 arches, and, after uniting into a single trunk on each side, give rise 

 to the aorta descendens. The existence of an anastomosis between 

 the trunks of the artery and that of the vein of each branchia was 

 indistinct ; but small branches went to the branchial filaments. 



"The pulmonary arteries arise from the trunk into which the 

 branchial veins unite on each side. The pulmonary veins open, on 

 each side, into the corresponding inferior vena cava. In addition, I 

 found, but only on the left side, that a vein arose from the posterior 

 vesicular end of the lung, which, uniting with a superior ovarian vein, 

 passed directly into the vena cava inferior, as Rusconi has represented 



