ORGANS OF THE BODY. 449 



laminated flattened species) consists of a slightly laminated layer of cili- 

 ated cells (1) (p. 149). Among these are scattered a certain number of 

 beaker cells, which are also present in the trachea and its ramifications, 

 according to Gegenbavr and Knauff. 



The nerves supplying the larynx are branches of the vagus, namely, 

 the Laryngeus superior, composed of fine medullated fibres principally 

 sensitive, and the /. inferior, formed of broad filaments, and essentially 

 motor. Their ramifications have in many cases microscopically small 

 ganglia connected with them. They are distributed to the muscles, the 

 perichondrium, and the mucous membrane. Their terminal plexuses 

 may be recognised in the latter, but not the ultimate ending of their 

 primitive fibrillse. 



Nothing unusual is to be seen in regard to the blood-vessels. The 

 lymphatics are numerous, and are arranged in the mueosa and sub- 

 mucous layer in a superficial and deep network, which are not, however, 

 sharply defined against one another in all cases (Teichmann). 



240. 



The trachea, with its branches the bronchi, may be described as a 

 ramifying tube, consisting of a strong fibrous tissue, in whose anterior 

 wall lie embedded the annuli cartilaginei. Thus the fibrous tube pre- 

 sents in the first place perichondrium, and then the ligamenta interan- 

 nularia connecting the half rings of the trachea one with the other, and 

 finally closing the cartilaginous canal behind the membrana transversa. 

 The latter is strengthened internally under the mucous membrane by a 

 thick layer of muscular bundles, running for the greater part transversely. 



The fibrous tissue of which the canal is principally formed possesses 

 besides an abundance of elastic fibres (p. 229). 



The tracheal cartilages belong to the hyaline species ( 107), and have 

 nothing remarkable about them. 



The muscular substance of the wind-pipe is made up of smooth fibres 

 ( 163). It is about '8-1 -2 mm. thick. The great abundance of elastic 

 tissue present throughout the whole respiratory apparatus, allows also of 

 the formation of beautiful elastic tendons, through which these muscles are 

 attached to the perichondrium on the extremities of the annuli cartila- 

 ginei. External to these transverse muscular, fibres there are frequently, 

 though not invariably, found a number of scattered longitudinal bundles 

 which take their rise from the fibrous wall of the canal (Koelliker). 



The mucous membrane of the trachea, 0'13 or 0*15 mm. in thickness, 

 contains a multitude of racemose mucous glands, in some instances small 

 and simple, in others large and complex, in which case the body of the 

 organ reaches deeper into the wall of the tube. The larger glands are 

 situated partly between the rings of the trachea, and partly in the pos- 

 terior wall, in which a regular layer of them presents itself. 



The surface of the mucous membrane is clothed with ciliated epithelial 

 cells, of 0*0594 mm. in height, interspersed with beaker cells. 



The trachea is also richly supplied with blood-vessels and lymphatics. 

 The latter are arranged in a superficial layer of minute canals, measuring 

 in diameter 0'0678 mm., lying in the mucosa, and taking principally a 

 longitudinal direction, and a deeper set of much larger tubes 0'0941 mm. 

 in diameter. The course of these stronger trunks is, at least, partly 

 transverse (Teichmann). The nerves of the part which are supplied by 

 the sympathetic and inferior laryngeal require closer study. 



