108 ON THE MOEPHOLOGICAL CONSTITUTION OF 



and more particularly to referring the perforation which gener- 

 ally characterises it to the system of dermal mucous canals. 

 The lachrymal canal is a metasomatomic opening. It is the 

 remaining portion of the cleft between the maxillary and 

 palatine visceral laminae. The lachrymal bone is situated at 

 the upper end of this cleft, at the extremity of that metasoma- 

 tomic space in which the eyeball is situated — viz. the orbit. 

 The lachrymal bone is therefore grooved or perforated by an 

 integumentary canal, which, as a portion of one of the original 

 clefts in the wall of the face, is retained in the adult as a pas- 

 sage for the secretion of the lachrymal gland. 



The most important cephalic neuractinapophyses are those 

 fibrous, cartilaginous, or osseous structures which support and 

 protect the nose, eye, and ear. They exhibit their fundamen- 

 tal character most distinctly in the cyclostomatous and 

 plagiostomatous fishes, in which they consist of sessile or 

 pedunculated cartilaginous cups or capsules attached to the 

 outer margins of the cranium. In the other vertebrata these 

 " sense-capsules," variously modified in form and texture, be- 

 come more or less involved in the wall of the cranium. In 

 their fundamental form they must be considered as parts of 

 the endo-skeleton, homologous in the hsemapod with those 

 parts of the dermo-skeleton of certain neuropods, such as the 

 crustacean, which carry the organs of sense, and are serially 

 homologous with its masticatory and ambulatory limbs. 



Professor Owen refers the " sense-capsules" to the 

 splanchno-skeleton. But the organs of hearing, vision, and 

 smell, are developed not from or in connection with the 

 mucous layer of the blastoderma, but from the so-called 

 " serous layer" — that is, from that superficial layer which pro- 

 duces the skin, its appendages, the cerebro-spinal axis, and the 

 primordial vertebral system. It appears to me that it would 

 have been more natural to refer the sense-capsules, as Do 

 Blainville did, to the dermal system ; but their histological. 



