52 LECTURE III. 



type to be further exemplified at this low step iu the series, but rather 

 be prepared for a divergence into individual peculiarities ; and this 

 is illustrated by the complex development of the visceral arches for 

 the support of the heart and gills, which are homologous to the 

 branchial arches in higher fishes. Yet the analogy of these parts in 

 the Lamprey, which Miiller has termed the cartilaginous basket of 

 the brauchiaj (xxi. p. 254.) to the modifications of the pleurapophyses, 

 hajmapophyses and their spines, constituting the ribs and sternum in 

 the air-breathing Vertebrates, is so close that we may be justified in 

 describing them in connexion with the vertebral column. 



Fore part of skeleton. Lamprey (Pt7ro7«j/3;on). 



Seven cartilaginous processes, analogous to pleurapophyses, but 

 homologous with epibranchials {Jig. 11. 48, 48), came off fi'om a car- 

 tilaginous tract on both sides of the chorda dorsalis, one below each al- 

 ternate neurapophysis (ib. ti) : after a short course outwards and down- 

 wards the process divides into three branches, one passing forwards, 

 one backwards, and the intermediate process (cerato-branchial, 47). or 

 continuation of the quasi-rib, downwards : the anterior and posterior 

 processes of contiguous ribs coalesce and form arches above the 

 branchial apertures (i, 2, to 7), which are circumscribed by similar 

 arches, formed below by analogous branches there given off" from the 

 cerato-branchial ; this then descends, bends inwards, dilates, and is 

 perforated ; then contracts and joins a broad and long cartilaginous 

 hypo-branchial (45), or quasi-sternum, typifying by its double row 

 of perforations that complex bone in birds. The anterior branches 

 of the first cerato-branchial unite to form a vertical arch, convex for- 

 wards ; the posterior pair (47') expand and unite to form the per- 

 forated cartilaginous case, lined by the pericardium, which contains 

 the heart : pursuing the analogy of this complex cartilaginous 

 branchial and cardiac skeleton with the thorax of higher Vertebrata, 

 we might regard the posterior processes of the ribs as foreshadowing 

 the costal appendages of birds. Homologically, the entire ajiparatus 

 answers to the branchial skeleton of higher fishes, a part which 

 Geoffroy St. Hilaire regards as a repetition of the thorax of air- 

 breathing Vertebrata, but which the metamorphoses of the Batrachia 

 prove to be a development of the visceral skeleton in immediate con- 

 nexion with the hyoidean arch. 



