RESPIRATION. 



29i 



the soft structures. This part is represented 

 transversely in Jig. 238, in which also the 

 disposition of the constituent cells may be 

 remarked to bear advantageously upon the 

 mechanical functions of the parts. As regards 

 the arrangement of these cells, this piece in the 

 framework of the gill-process may be divided 

 into two parts, by a longitudinal "line, on the 

 outer side of which the long axes of the cells, 

 which are oblong, are directed transversely 

 with respect to the inner: the axes of the 

 cells are parallel with that of the processes of 

 which they are the constituents parts. This 

 arrangement is most distinctly marked in 

 those genera in which the skeleton is little 

 calcified. Functionally considered the piece 

 occupying the blunt edge of the process de- 

 termines its penknife-like contour, and confers 

 strength and straightness of direction, thus 

 favouring the contact between the respiratory 

 foliage and the surrounding medium. It dis- 

 charges the passive office of sustaining the 

 soft structures and of extending the plane 

 superficies over which the branchial blood- 

 vessels are distributed. 



The internal or acute margin of the bran- 

 chial process conceals, in the recent structures, 

 under the lab\ rinth of the superimposed re- 

 spiratory membrane, a skeletal mechanism of 

 singular novelty and beauty (f, Jig. 238.) 

 From the innermost side (near its root) of the 

 denser piece which lies parallel \\ith the outer 

 margin of the lamella, a less dense, more 

 transparent, and more cartilage-like process 

 (d,Jig. 238.) rises, to advance along the in- 

 ternal margin of the lamella from its base to 

 its extreme apex. From either side of this 

 process, at right angles, processes (f and 

 cc), still more slender, delicate, and trans- 

 parent, are detached, to follow for some dis- 

 tance the circumference or free margin of the 

 membranous leaflet on which the vascular 

 network is outspread. 



This part of the skeletal fabric of the 

 branchial lamella is actively and importantly 

 concerned in the mechanism of the respira- 

 tory function. It is to the branchiae what 

 the ribs are to the mammalian lungs. The fine 

 extremities of these transverse portions, as 

 seen in c, c, taper off into a species of 

 curly fibre, which travels accurately along the 

 extreme margin of the membranous leaflets to 

 the point () at which the latter rest upon 

 the flat surface of the osseo-cartilage of 

 the obtuse margin. The axis which sup- 

 ports this system of elastic " ribs " (in sec- 

 tion at c and d) exhibits under the mi- 

 croscope a median transverse line appa- 

 rently filled \\ith an oleaginous fluid, which 

 communicates with the moniliform system of 

 cells, occupying the axes of the curved 

 pieces (c, c), where probably it performs the 

 two-fold office of mechanically distending and 

 nourishing the parts. No vestige of an Ha- 

 versian order of canals can be discovered in 

 any portion of this branchial framework. 

 The calcareous granules of Tomes are dis- 

 tributed irregularly over the parietes of the 

 cartilage cells. It is not easy to misappre- 



hend the office which devolves upon this 

 apparatus. By means of two needles the 

 recent branchial ray may be separated into 

 two longitudinal halves, to the inner of which, 

 exclusively, the membranous leaflets remain 

 adherent, a circumstance which illustrates the 

 anatomical connection between these softer 

 parts and the delicately adjusted framework 

 of the internal border of the leaflet. The 

 elastic transverse processes (c, c), from their 

 constrained curved position, constantly tend 

 to straighten themselves, and to convert 

 the curved into a direct line of action. This 

 straightening tendency, which is a constantly 

 and unremittently operating force, constitute 

 the immediate agency under which the tang- 

 ling, folding, or crumpling of the leaflets bearing 

 the capillary network is rendered impossible. 

 Under the ceaseless operation of this resilient 

 property, the true breathing surface is regu- 

 larly maintained in a state of uniform exten- 

 sion, and that at a degree of lightness, 

 measured with wonderful precision, to suit 

 the exigencies of structures so surpassingly 

 refined. A superficial consideration indeed 

 might have sufficed to render it improbable, 

 that a system of blood- channels of such ex- 

 treme delicacy as that which constitutes the 

 breathing apparatus of fishes could exist un- 

 injured, unless by aid of a basis of support at 

 once appropriate in its physical qualities and 

 mechanical disposition. 



Morbid anatomy of the lungs and air pas- 

 sages. It is possible in the space here al- 

 lowed to do little more than to enumerate 

 the pathological conditions to which these 

 parts are liable. The diseases of the lungs and 

 bronchi since the era of Laennec have re- 

 ceived a considerable share of the attention 

 of pathologists. The normal anatomy of the 

 lungs is now known with precision. The 

 characteristics of the alterations of structure 

 which in disease they undergo, within recent 

 years have also been defined with correspond- 

 ing precision. The community between the 

 bronchial and pulmonary circulation established 

 by the recent researches of Dr. Heale, will 

 probably oblige pathologists to modify their 

 views with respect to the supposed distinct- 

 ness and independence of the diseases of the 

 lungs and the bronchi. The following tabu- 

 lated arrangement, as given by Rokitansky, in 

 the 4th vol. of his Pathological Anatomy, ex- 

 hibits the abnormal conditions of these parts 

 in lucid summary. 



1. Deficiency and excess of formation. 



2. Deviations in size. 



a. Morbid dilatations of the air passages. 



b. Dilatations of the larynx and of the 



trachea. 



c. Dilatation of the bronchi. 



d. Contraction of the air passages. 



e. Hypertrophy and Atrophy. 



3. Deviations in form. 



4. Deviations in position. 



5. Interruptions of continuity. 



6. Diseases of texture. 



A. Diseases of the mucous membrane and 

 of the subjacent areolar tissue. 



a. Ilyperiemia and Anaemia. 



b. Inflammations of the mucous membrane. 



u 2 



