500 PROF. RAY LANKESTER ON THE HEARTS OF 
ventricular curtain into the auricle); but instead of ending abruptly in the auricle, it 
is continued across the sinu-auricular floor in the form of a strong fibrous ridge, and 
can actually be traced into the tough fibrous walls of the large vena cava, which, sur- 
rounded by liver, opens mesially into the hinder part of the sinu-auricular cavity. 
It would thus seem that the basal fibro-cartilage, ‘“‘ eine Vorrichtung, die noch bei 
keinem Wirbelthiere beobachtet wiirde,” as Hyrtl remarked when first describing it in 
Lepidosiren, has its most extensive development in Ceratodus (it is shown throughout 
its course in fig. 4), and its smallest in Protopterus; whilst in Lepidosiren it acquires a 
special relation to muscular trabecule of the auricle, which gives it a share in the 
formation of the imperfect auricular septum present in that alone of the three genera 
of Dipnoi. 
IJ. Heart or Proropterus (LEPIDOSIREN) ANNECTENS. 
Professor Owen, in the description of the anatomy of this form, has not given special 
illustrations of the general appearance and interior structure of the heart ; and, I believe, 
it has not been figured by any later writer. Ina monograph which contained so much 
that was new and of the greatest importance, it is not surprising that the smaller 
details of one organ should be passed over. The main features of the structure of the 
heart (excepting the basilar fibro-cartilage) were briefly described by Owen ; his atten- 
tion was especially given to the structure of the conus arteriosus, concerning which he 
notes the absence of watch-pocket valves, the spirally-twisted shape, and the presence 
of longitudinal folds or valves. 
In figs. 8, 9, 10, 11, 12 I have given drawings of the entire heart of Protopterus' 
and of dissections. 
In figure 8 a front view of the heart removed from the pericardium is given. It is 
more symmetrical than that of Ceratodus, and differs most markedly from the latter in 
the presence of large auricular appendages, and in the constriction of the neck of the 
arterial cone. A fibrous band connects the apex of the ventricle with the pericardium, 
as in Ceratodus. 
On turning the same heart we obtain a more complete view of auricle and sinus (fig. 9). 
The sinus is elongated posteriorly, and has tough fibrous walls where it becomes con- 
tinuous with the large median vena cava. Towards the auricle its walls become much 
more delicate, and are loosely folded in the collapsed condition. Externally there is 
no marked constriction between the sinus and the median portion of the auricle. The 
lateral expansions of the auricle are very voluminous, and are vesicular or even digi- 
tate. ‘Chey extend around the ventricle, and fit with their upper processes into the 
‘ I must point out here that the observations recorded in the present paper on the hearts of Ceratodus, 
Protopterus, and Chimera haye, owing to special circumstances, been made on eacised hearts. I have not, 
therefore, in any case entered into the question of the number and position of the openings of vessels into the 
auricular sinus, nor of those from the conus. 
