102 ORIGINAL AllTICLES. 



bouuclary. The tibio-tarsal rete niirabile of this wingless bird is 

 therefore unipolar. In tlie iwWj developed rete of Struthio and its 

 congeners it is however bipolar ; each of its few constituent branches, 

 inserts itself into the trimk of the tibialis some inches above the 

 tarsal point. 



I ha^e also recorded the attempt at formation of rete mirabile in 

 short-legged birds, and among them a very singular case in Apteno- 

 di/tes {Spheniscus). 



Among the mammalia the number of hitherto kno^vn* retia 

 mirabilia and plexuses has been considerably increased ; the arteries 

 of the anterior and posterior extremities of many Pachyderms are 

 provided with them, as I have observed in the Peccary, Tajacu, 

 Phacochoerus, Tapir, Hyrax {cnpensis and syriacus), and in the com- 

 mon pig. I have little doubt but that anatomists, who are so very 

 fortunate as to live near the Zoological Gardens, London, or the 

 Jardin des Plantes, Paris, will be able in time to include among the 

 number, the names of such grand animals as JElephas, Rhinoceros 

 and Hippopotamus, which, like many other prodigies of ' fei^ax mon- 

 strorum Africa' (Plin.) will never come within my reach. 



Among the true Quadrumana, there is no rete mirabile, but a 

 strange tendency towards the formation of one is to be found among 

 the thumbless apes, as in Afeles, where it manifests itself in the divided 

 aspect of the elsewhere single and undivided arteries. 



In the Prosimii, the collateral branches of all the main trunks 

 jut out like a series of rays, so that a number of them have quite 

 the appearance of tufts of tassels, a disposition which was discovered 

 by Johannes Miiller in other animals, and denominated by him, ' Eete 

 mirabile unipolare diffusum,' (as in Thjnnus) ; this curious origin of 

 numerous side branches in the form of tufts or tassels, occurs in 

 Lemur, Galago, Lichanotus, whilst in Tarsius spectrum and Stenops 

 gracilis, true plexiform retia mirabilia occiu' in the brachial and the 

 crural arteries. 



Ilitlierto retia have not been found among the Carnivora ; the first 

 instance I saw was in the genus Viverra, where it occurs in the 

 cutaneous branches of the crural artery ; it accompanies the saphenous 

 nerves, and forms a very slender and pretty rete saphemun, which 

 extends through the leg as far as the ankle. In the Marsupials 

 plexiform retia mirabilia are deficient in the limbs, but they are 

 found well developed in the palatin and inferior maxillary arteries. 



The special function of these retia appears still to be buried in 

 obscurity, but still it may not be useless to collect thus a larger 

 series of facts : some day or other, doubtless, they will be weighed in 

 the balance of physiological reason. 



* Since tlie time of Carlisle (Pliil. Trans. 1800), who discovered them in the arm 

 of the 81oth, they have been ol)sorvcd (by Vrolik) in Sicnops ; (by Baer) 

 among the Whales; (by Koscnmullcr) in the Senl ; (by Allman, Kept. Brit, 

 Afpoc. 1844) in Dasypus, and (by myself, Proceed. Imp. Acad. Vienna, vols. v. vi.) 

 in Myi'inecophoga, Mnnis, Chlumijdophorus, Ornitlwrh>j7ichus, and 2'richecus. 



