760 SPECIAL HISTOLOGY. 



structed in the same simple manner as the excretory ducts of the lach- 

 rymal glands, consisting merely of a dense connective tissue mth nu- 

 merous networks of fine elastic fibres, particularly abundant in the 

 lachrymal canals, which appears to be a continuation of the mucous 

 membrane of the nose and of the conjunctiva, and of an ejntlielium 

 which, in the lachrymal canals, is of the squamous kind, and in the 

 lachrymal sac and nasal duct is furnished with vibratile cilia, as in the 

 cavity of the nares. The muscles of the globe of the eye and of the 

 eyelids, as well as the musculus JTorneri, are all composed of trans- 

 versely striped muscular fibres, and together with their tendons, pre- 

 sent no differences from those of the trunk and extremities. The fascia 

 hulbi oculi s. Tenoni is a true fibrous membrane, and the trocJilea is 

 formed principally of dense, connective tissue, in which only a few 

 cartilage cells can be seen. 



The vessels of the organs described in this section present little 

 worthy of remark. Excepting those of the muscles and skin, they are 

 most abundant in the palpebral conjunctiva, in which they chiefly enter 

 the jJapili'-v, and in the next place in the lachrymal glands and the 

 caruncula lachrymalis. The sclerotic conjunctiva also contains numerous 

 vessels, and the Meibomian glands within the tarsi are also surrounded 

 by a few. Except in the skin of the eyelids, lymphatics have only been 

 demonstrated by Arnold in the conjuyictiva sclerotica;, where they form, 

 at the border of the cornea, a closer, and more externally a looser 

 plexus, passing outwards in several small trunks. The palpebrce and 

 conjunctiva are everywhere well supplied with nerves, but their rela- 

 tions have been minutely examined only in the conjunctiva. In this 

 membrane, in Man, I have found terminal plexuses as in the external 

 integument, with numerous divisions of fibres, 0-001-0-006 of a line 

 thick, extending up to the margin of the cornea, together with pretty 

 clear indications of loops and free terminations. Besides which, in one 

 instance, there were presented, towards the palpebral conjunctiva, pecu- 

 liar " nerve-coils," 0-02-0'028 of a line in size, into which a single 

 nerve-fibre usually entered, whilst 2-4 were given off from it [vid. " Mik. 

 Anat." II. 1, p. 31, Fig. 13, A, 3). The relations of the nerves of the 

 lachrymal apparatus are entirely unknown. 



§ 231. Physiological remarks. — The eyeball is not developed from a 

 single point as a whole, but arises from the conjunction of formations, 

 proceeding on one side from the central nervous system, on another from 

 the skin, and, thirdly, from the parts lying between the two. In the 

 Chick, the 'primitive ocular vesicles arise before the commencement of 

 the second day, from the primitive cerebral vesicle or the anterior cere- 

 brum, in the form of two protrusions, at first sessile, but afterwards 

 having a hollow peduncle — the rudiment of the optic nerve. At the 



