344 ON THE ANATOMICAL PECULIARITIES 
In structure, this part of the alimentary canal differs 
considerably from the oesophagus and stomach. The exte- 
rior membrane, indeed, like that of the latter, is peri- 
toneum ; and between this and the inner membrane there 
is interposed a layer of muscular fibres, with circular dis- 
position, about three lines, or J of an inch thick, and giv- 
ing proportional firmness to the intestine. But the inter- 
nal membrane is very different in appearance and phy- 
sical characters ; on the first sight it appears like a honey- 
comb net-work of smooth fibres intersecting each other, 
and forming large pentagonal meshes, or cells ; and this 
arrangement unquestionably it was which induced the late 
Dr Monro to denominate this of the sturgeon reticular. 
It is not worth while to dispute the propriety of this as a 
general character of the appearance which the inner sur- 
face of the duodenum presents. I shall rather endeavour, 
by precise description, to communicate as distinct an idea 
of it as possible ; and, when the arrangement is under- 
stood, it is of little moment by what name it is denomi- 
nated. 
A given space of this surface, when minutely examined, 
is found to consist of numerous bands of animal matter, 
about the breadth of derning needles, and round and 
smooth on the surface, intersecting each other in directions 
not very definite, but so as to form a series of trapeziums 
and irregular pentagons. These bands may be considered 
as primary. The trapezoidal and pentagonal spaces which 
they enclose, present again surfaces intersected in like 
manner by much more minute bands, some not exceeding 
the size of sewing needles, and some as minute as hairs. 
The interstices of these intersecting or reticular bands, are 
of various sizes. Those of the primary walls are from 
1| to 2 fines in superficial extent ; those of the secondary 
